Since the Wei and Jin Dynasties, a major change in the tomb structure is that the tomb passage has become a highly valued construction area outside the tomb chamber. In the late Northern Dynasties, tomb passage murals that reflected this change also came into being in the northern region. This article focuses on the relationship between "technology" and "art", and attempts to reveal two distinctive burial area decoration traditions developed in the eastern region centered on Yecheng and the Guanzhong region centered on Chang'an, based on the two tomb passage construction techniques of "staircase" and "hole-patio" respectively. The former takes ceremonial figures as the basic theme, and expands the subject matter according to the wall conditions to highlight the identity and majesty of the tomb owner; the latter continues the decorative tradition of the Sixteen Kingdoms and relies on the passage area in the tomb passage to construct a spatial image of "guarding the heavy gates".

Since the Wei and Jin Dynasties, tomb architecture and decoration traditions have gradually undergone a series of changes. One of the most significant changes is that in large tombs, the tomb passage has gradually become a highly valued construction area outside the tomb chamber. Especially in the high-level tombs in the northern region from the late Northern Dynasties to the Sui and Tang Dynasties, not only did the length of the tomb passage increase rapidly, often reaching tens or even hundreds of meters, but tomb passage murals that were compatible with this type of tomb component also came into being.

In response to this phenomenon, the academic community has previously focused on the tomb passage architecture itself, discussing the transformation of the Chinese burial system from the "Han system" to the "Jin system" and its extended development during the Southern and Northern Dynasties; or they have focused on the content of the tomb passage murals themselves, discussing related systems such as "Lu Bu" and "Yi Zhan". Although both types of research are concerned with the important topic of hierarchy and have achieved quite fruitful and important academic results, an issue that is easily overlooked is that before the late Northern Dynasties, although the status of the tomb passage was already very prominent, murals were rarely applied on both walls of the tomb passage. This shows that the two did not occur at the same time, and their purposes were not necessarily consistent.

Inspired by Lin Weizheng and Zheng Yan's research on the relationship between murals and architecture, the author realized that murals originally existed as interior decorations of tomb buildings, and changes in architectural space will greatly affect the subject selection and layout of murals; and understanding "pictorial space" in connection with the "architectural space" in tombs is the key to understanding the content and form of tomb murals in the Northern Dynasties and even the Sui and Tang Dynasties. In view of this, this article focuses on the relationship between "technology" and "art". On the basis of the research results of predecessors, it examines how tomb passage murals responded to different tomb passage construction traditions and the two technical means that were ultimately formed, and how they developed decorative systems and expression themes in different regions, and finally merged into a stable system for the construction and decoration of high-level tomb passages in the Sui and Tang Dynasties.

1. Two types of long tomb passages as construction techniques

A tomb passage is a special passage connecting the ground surface with the underground tomb chamber, with vertical shaft passages and slope passages being the most common. Zhu Lei has made a relatively comprehensive summary of the reasons and basic functions of the sloping tomb passages involved in this article: "The tomb passages should have been created to cooperate with the construction of large tombs. Their function is to facilitate the workers' walking up and down, to unearth and transport building materials and funerary objects inward, and to lower coffins and bury the deceased during funerals." As for the sloping tomb passages after their emergence, as an integral part of the tomb structure, the direction of their changes should depend on the actual needs of different eras and the evolution trend of the entire tomb culture. Therefore, they should first be placed in a long-term context for observation.

Archaeological discoveries in the middle and lower reaches of the Yellow River show that as early as the Shang Dynasty, a few high-ranking noble tombs had already shown precedents of combining sloping tomb passages with vertical pit burial chambers. But overall, large tombs from the Shang and Zhou Dynasties to the Han Dynasty always focused on the tomb chamber. Even during the Han Dynasty when chamber tombs became the mainstream and the decorative trend was on the rise, images in the form of murals, stone carvings, etc. were mainly applied to the four walls and top of the tomb chamber. During the Wei and Jin Dynasties, the burial system and funeral customs underwent a tremendous transformation from the "Han system" to the "Jin system". Its manifestation in the burial form was summarized by scholars such as Jin Hongxiang and Wang Yu as follows: single-chamber tombs gradually replaced multi-chamber tombs as the mainstream, and the size of tomb chambers was greatly reduced; at the same time, the size of tomb passages was becoming increasingly prominent. For example, the tomb passages of the Cao Wei royal family tombs in the Central Plains occupied 2/3 to 3/4 of the total length of the tomb. This trend of focusing on the tomb passage and neglecting the tomb chamber undoubtedly provided new historical conditions for the innovation of tomb construction and decoration traditions. During the Eastern Wei, Western Wei, Northern Qi and Northern Zhou dynasties, high-level tombs pioneered the practice of painting large areas of murals in tomb passages. Tomb passages then became one of the core areas of tomb decoration, and this practice reached its peak during the Sui and Tang dynasties.

Figure 1 A bird's-eye view of Cao Xiu's tomb in Luoyang

During the above-mentioned transformation process, two types of tomb passage forms were popular for a long time. One type is that the walls on both sides of the tomb passage are stepped inward from top to bottom, forming a "large mouth and small bottom" shape [Figure 1]. This architectural style originated in the Shang Dynasty Tombs in Anyang and was first used on the walls of tomb chambers. During the Western Han Dynasty, it was extended to the walls of tomb passages in the Chang'an area. It was quite popular in the large tombs in Luoyang during the Western Jin Dynasty. Until the late Northern Dynasties, it still had traces in the Bingzhou area (now Taiyuan, Datong in Shanxi and Baoding in Hebei). The other method is to build tunnels and patios in the tomb passage. The tunnels are usually arched earth cave structures, and the patios are similar to vertical shafts that go straight to the ground. The two are usually the same in number and are distributed in groups with staggered intervals [Figure 2]. The skylight seems to have originated in the Qin Tomb in Xianyang, and later in the early Western Han Dynasty, it was combined with the tunnel and appeared at the connection between the tomb passage and the burial chamber in the tombs near Chang'an. From the Sixteen Kingdoms to the heyday of the Tang Dynasty, long tomb passages with multiple skylights and passages flourished in the Guanzhong region, and at one point in the middle and late Northern Wei Dynasty, they influenced some tombs in Pingcheng (now Datong) and Luoyang. Liu Weipeng made an important discovery: as passageways and patios became increasingly mature and popular in the Northern Zhou Dynasty, the practice of multiple steps on the walls of the tomb passages no longer appeared. This fully demonstrates that there is likely to be a forward-and-backward substitution or conversion relationship in construction technology between the two, and the reasons behind this are worth exploring.

Figure 2 Orthographic projection of Yuwen Jue's Tomb in the Northern Zhou Dynasty in Xi'an

The relationship between the two types of tomb passage forms and the status of the tomb owner

In view of the multi-layer stepped construction method of tomb walls since the Eastern Zhou Dynasty, especially in the Western Jin Dynasty, and the use of "skylights" and "passageways" in long tomb passages since the Northern Dynasties, especially in the Tang Dynasty, the academic community has always judged the status of the tomb owner based on the presence or absence and number of the two, and even directly regarded their function and significance as symbols of status. The formation of this understanding may be based on burial materials from a specific era or local area. However, after comprehensively sorting out the development of the two types of tomb passage forms, the author found that this understanding is not valid.

First of all, these two types of tomb passages are not limited to use in high-level tombs. For example, during the Eastern Han Dynasty, some high-level tombs in the Mangshan Imperial Mausoleum in the capital Luoyang adopted a method of having tomb walls that were stepped inward 1-3 levels, and similar practices were also frequently seen in small and medium-sized tombs in the Chang'an area. The fact that these tombs, whose owners had vastly different identities and statuses, shared a common plan for the construction of the tomb passages seems difficult to explain in terms of hierarchy. Secondly, although these two types of tomb passage forms are scattered in Shaanxi, Henan, Shanxi and other places, they are most densely distributed and last the longest in the Guanzhong region. There are also many examples of intertwined coexistence in tombs from the Western Han Dynasty to the Sixteen Kingdoms period. This development process is more like a continuation of a technological tradition rather than a symbol of status. Again, taking the tombs with patios and passageways as an example, from the Western Han Dynasty to the Sixteen Kingdoms period, the users of this type of tombs included royal relatives, middle and lower-level officials, and small and medium-sized landlords. It was not until the Northern Zhou Dynasty that the users of this type of tombs were mainly limited to royal family members and high-ranking officials of the ninth degree. However, the number of patios and passageways was between 3 and 6, which strictly speaking could hardly reflect the differences in the identities of the tomb owners.

In fact, there are doubts in the academic community regarding the above-mentioned cognition. The excavators of the Chu Tomb in Geling, Xincai once pointed out that "the number of steps (in the tomb) is directly related to the scale of the tomb, but from the published information, it does not seem to have much to do with the identity and status of the tomb owner." Geng Shuo also came to a similar conclusion from his research on the large tombs of the Wei and Jin dynasties in Luoyang. In his opinion, the number of steps in these tombs mostly depends on the depth of the burial chamber. As for long slope cave tombs, depth is only one of the influencing factors. Xu Feihong revealed the connection between the length of the Northern Zhou tomb passage and the number of passages and patios: "The area of the (Northern Zhou) tomb chamber is limited due to the use of earth holes. Therefore, the practice of distinguishing the levels by the area of the tomb chamber is obviously difficult to implement. The level of the tomb can only be demonstrated by the length of the tomb passage. ... The surge in the number of patios in Northern Zhou tombs should be a chain reaction after the length of the tomb passage is linked to the identity of the tomb owner." A large amount of archaeological data confirms this intrinsic connection: in the Luoyang area, among the burial tombs of the Eastern Han emperors in the Mangshan Mountain, only those with passages longer than 20 meters are stepped; in the Western Jin Dynasty tombs, those with passages longer than 15 meters usually have 1-7 steps. In the Guanzhong area, among the tombs of the Sixteen Kingdoms, only those with a length of more than 20 meters had multiple steps and 1-2 sets of passageways and patios. Tombs less than 15 meters long had no steps or passageways or patios. Northern Zhou tombs with a length of more than 30 meters mostly had more than 3 sets of passageways and patios, while tombs between 20 and 30 meters long mostly had 2-3 sets of passageways and patios.

From the above, we can know that the use of multi-layer stairs, passages and patios in the tomb passage is actually closely related to the scale of the tomb passage, especially the length of the tomb passage. The size of a tomb largely reflects the identity of the tomb owner, leading many scholars to regard the presence or number of multi-layered stairs, passages, and skylights as symbols of rank. After clarifying this point, the question that remains to be solved is: Why are these two structural forms closely related to the scale of the tomb passage? What are its causes and functions?

Architectural historian Guo Qinghua once pointed out: "Ancient Chinese tombs must first be durable. Therefore, structural details and construction technology are the core factors that determine and restrict everything in tomb architecture." Based on this inspiration, the examination of the structural details and construction technology of the "staircase" and "through-hole-patio" tomb passages may be the key to solving the problem.

The technical causes and practical functions of the "staircase" type tomb passage and the "hole-patio" type tomb passage

As mentioned earlier, during the Wei and Jin Dynasties, the tomb passage had become a key area in tomb construction, and the high pursuit of the scale of the tomb passage brought new challenges to the construction technology. This is because when the tomb passage is excavated to a certain depth and length, the original balance between the soil is broken, and it is very easy for the side wall to collapse due to the pressure of the tomb wall. This phenomenon is not uncommon in existing archaeological discovery materials. For example, the large Northern Wei tomb discovered in Luoyang, Henan, which is speculated to be the tomb of Emperor Jiemin, has a 39.7-meter-long tomb passage with vertical walls without steps, caves, or skylights. During the excavation and cleaning, it was discovered that there were several column holes on both walls of the tomb passage near the tomb door, which were left by wall pile reinforcement and repair, proving that collapse had occurred during the construction process. It can be seen that ensuring the stability of the tomb passage is the primary issue in the construction process of this type of tomb. Regardless of whether it is the stepped construction method or the through-hole-patio construction method, they are essentially tomb passage construction techniques to prevent the collapse of the two walls.

Regarding the technical causes of the stepped tomb walls, Zhu Chenlu and Duan Qingbo mentioned in their discussion of large and medium-sized earthen tombs of the Western Han Dynasty: Compared with the steep pit walls formed by digging vertically from the ground surface to the bottom of the tomb, the stepped tomb walls can more effectively decompose the earth pressure above the ground. This is highly consistent with the principle of open-cut slope reduction technology widely used in modern underground engineering to prevent landslides. The tomb of Cao Cao, discovered in Anyang, Henan Province in the 25th year of Jian'an in the Eastern Han Dynasty (220 AD), clearly reveals this purpose. The tomb passage is 39.5 meters long, 9.8 meters wide at the top and 4.1 meters wide at the bottom. The left and right walls near the tomb door are in a seven-layer stepped structure that extends downward. The sloping ground on both sides is reinforced with rammed earth, and left and right opposing buttresses are built at the intersection of the two walls of the tomb passage and the tomb door. There are also five wooden pillars inside the buttresses as keels [Figure 3]. Buttresses were first used in tombs during the Wei and Jin Dynasties. They are additional components built to balance the thrust of the vaulted structure on the wall. Even in modern slope engineering, buttress retaining walls are still an effective means of reinforcing pit walls. Therefore, these measures taken in Cao Cao's tomb were obviously also to reduce the pressure on the wall, stabilize the load-bearing wall, and avoid the collapse of the long tomb passage.

Figure 3. Map of the passage to Cao Cao’s tomb in the Eastern Han Dynasty in Anyang

Different from the mechanical principles used in the stepped construction method, the construction technology of building passages and patios in the hidden arches is another way to achieve the purpose of consolidating the tomb passage. First of all, according to soil geographical analysis, the soil in Guanzhong area is mainly loess-brown soil with obvious clay characteristics, so it is quite suitable for building structures such as tunnels underground. This special soil condition also explains why tunnels and patios flourished in the Guanzhong region. Secondly, after the tunnel is excavated, the soil in the center of the tunnel is removed, and the soil around the tunnel needs to reach stress balance again. At this time, part of the soil may be in a plastic state, which may cause the surrounding soil to slip, relax or be damaged. To avoid this risk, the tunnel must adopt an arch structure to disperse and transfer pressure to improve the bearing capacity of the structure. However, the key to using this technology is to limit or shorten the length of the passage, so the passages and patios in the tombs always need to be staggered and spaced short. Taking the most typical Northern Zhou tomb passage as an example, each tomb, depending on its size, has a passageway that is usually 1.7-2.5 meters long and 1-1.5 meters wide; the patio is usually 3-4 meters long and 1-1.5 meters wide. The reason why the scales of the patio and the passage are so regular can only mean that the tomb builders at that time had a full understanding of the mechanical principles involved.

Not only that, the invention of the skylight and through-hole technology is essentially an innovation of the previous technical tradition. Its real intention is far more than just to ensure that the tomb passage is sturdy and durable, but also to improve construction efficiency. As scholars such as Fu Xinian pointed out: The long sloping tomb passage requires a large amount of earth when excavating, and the excavation method that combines open-air patios and underground tunnels can greatly reduce the amount of earth excavated, thereby cleverly reducing the total amount of work; and, because the patio increases the construction working surface, it can accommodate more people to work and enter and exit at the same time, which greatly improves the construction progress and can shorten the construction period by nearly half. From the common footrest facilities on the left and right walls of many tomb patios, one can imagine the situation of many people working on the tomb passage at the same time. Take the tomb of the Tuyuhun princess and General Ruru, which was discovered in Xi'an, Shaanxi Province in recent years and was buried together in the seventh year of Datong in the Western Wei Dynasty (541) as an example. The tomb is a double-chamber earthen cave tomb with a long sloping tomb passage and four groups of passageways and patios. There are 7-8 footwells on the left and right walls of the first to third patios, and there are as many as 16 footwells on the left and right walls of the fourth patio connecting the corridor and the tomb chamber. It is obvious that the tomb was also used for people working in the tomb chamber to go up and down. Because the tunnel-skylight style tomb passage is more scientific and labor-saving, its technical advantages are obvious. Therefore, this technology was still used until the Sui and Tang dynasties, becoming one of the most important formal features of high-level tombs at that time; while the stepped tomb passage came to an end in the late Northern Dynasties.

The influence of decoration demand on the construction technology of tomb passage

It is worth noting that some high-level tombs in the northern region during the Eastern Wei, Northern Qi, Western Wei and Northern Zhou dynasties all showed a strong interest in tomb passage decoration. This artistic tendency may have also contributed to the rise and fall of the two types of tomb passage technologies. When discussing the mural tombs of the Northern Dynasties, Sui and Tang Dynasties, Wu Hung pointed out that the reason why the scale of the tomb passage continued to expand over hundreds of years was because it was given an increasingly larger image display function, and the driving force was people's growing enthusiasm for the "exhibition space" outside the tomb chamber. This view tells us that we cannot ignore the influence of factors other than construction technology, such as decorative needs, on the shape of the tomb passage. Archaeological discoveries do show signs that tomb passage murals once influenced the choice of construction technology.

First of all, the tomb of Princess Ruru Lu Chidi Lian, which was built in the eighth year of Wuding in the Eastern Wei Dynasty (550), and the Wanzhang Northern Dynasties mural tomb, which was built around the middle period of the Northern Qi Dynasty, both located in Ci County, Hebei Province, are of extremely high specifications. However, due to the need to paint large murals, neither tomb had a stepped passage. Instead, they adopted the oblique excavation technology with a wide mouth and a narrow bottom to ensure the stability of the passage. This technology has frequently appeared in small and medium-sized Han tombs in the Guanzhong area. It can also reduce wall pressure and avoid landslides. However, for the Wanzhang Tomb, whose tomb passage is 37 meters long, the effect of this technology is far from satisfactory. Therefore, the tomb used a more special method of tomb wall reinforcement - building adobe walls and padding soil with cypress frames on both sides of the tomb passage to increase the wall strength. Another example is the tomb of Xu Xianxiu, King of Wu'an in the second year of Wuping in the Northern Qi Dynasty (571), which was discovered in Taiyuan, Shanxi. The tomb passage is 15.2 meters long and also uses the oblique excavation technology for painting large ceremonial objects. In order to ensure the safety and stability of the tomb passage, the craftsmen had to build two passageways and a patio in it. It is not difficult to see that, precisely because the stepped tomb passage technology could not meet the new demand for painting large ceremonial murals in high-level tombs, the craftsmen had to painstakingly superimpose a variety of tomb passage reinforcement technologies in order to achieve the goal of maximizing the painting area.

Secondly, if we turn our attention to the Guanzhong region in the west, we will see another interesting phenomenon. Before the Northern Zhou Dynasty, tombs in the Guanzhong region had long maintained the coexistence of two types of tomb passages: stepped type and tunnel-patio type [Figure 4]. Moreover, the intention to decorate the tomb passage had already clearly emerged at that time, but it had not yet taken the form of painting. However, when the Northern Zhou tombs changed the previous system and began to paint large areas of murals in the tomb passages, the original stepped tomb passage construction technology disappeared without a trace. Therefore, we have reason to believe that it was precisely because of the need to paint murals in the tomb passage that the tomb builders of the Northern Zhou Dynasty focused on developing the construction technology of the passage-patio and abandoned the stepped construction technology.

Figure 4 A bird's-eye view of Tomb No. 298 of the Sixteen Kingdoms in Dizhang, Xianyang

In summary, building stairs, passages and patios are the main construction methods commonly adopted in the construction of tomb passages since the Han and Wei Dynasties. As tangible representations of tomb passage construction technology, they are not symbols of the tomb owner's status, but are based on the actual needs of strengthening the tomb passage and improving construction efficiency. Their specific usage depends on the size of the tomb passage. Moreover, after murals began to be painted in tomb passages, the need for decoration further promoted the selection and alternation of these two techniques. Eventually, tomb passages with multiple skylights and multiple passages flourished during the Sui and Tang dynasties, until the tradition of long tomb passages in aristocratic tombs declined during the middle and late Tang dynasties, and the passage-skylight technology was no longer useful.

2. Two regional decorative traditions based on two types of tomb passage technologies

The glorious tomb decoration tradition of the Han Dynasty gradually died down in the late Eastern Han Dynasty and gradually revived after the Western Jin Dynasty. In the late Northern Dynasties, mural tombs in the eastern and western parts of the northern region pioneered the large-scale decoration of tomb passages with images, and developed two sets of distinctive regional decorative traditions. In the east, with Yecheng (now Ci County, Hebei Province and Anyang, Henan Province) as the center, a tomb passage image system with large ceremonial figures as the basic theme was formed during the Eastern Wei and Northern Qi dynasties, and radiated to Jinyang (now Taiyuan) and surrounding areas; in the west, with Chang'an as the center, a tomb passage decoration theme with wooden structures such as gatehouses and images of ceremonial guards with swords as the basic elements was formed during the Western Wei and Northern Zhou dynasties, and it influenced the Yuanzhou (now Guyuan, Ningxia) area.

Many scholars have noted the significant differences between the two regional decorative traditions, but there is no consensus on their causes. Zheng Yan once pointed out that "the tomb passage decorations of the Northern Qi and Northern Zhou tombs may not have a common model followed from an earlier era"; Li Meitian speculated that the Guanzhong-centric concept caused the region to accept the new cultural trends of the Southern Dynasties later than the Yecheng region. The author believes that the differences in the content and configuration of the tomb passage murals in these two areas should be inextricably linked to the different tomb passage forms formed by the use of different construction techniques.

The Tomb Passage Form and the Configuration of Mural Paintings in the Eastern Wei and Northern Qi Mural Tombs

According to Yang Jiawei's statistics, there are 39 mural tombs in the Eastern Wei and Northern Qi dynasties, of which 7 have murals painted on the tomb passages. Zheng Yan divided these tombs into two categories based on the shape of the tomb passages. The first type is concentrated in the Yecheng area and can also be found in Jinyang, represented by the tomb of Princess Ruru and the Northern Dynasties mural tomb in Wanzhang mentioned above. The entrance of the tomb is wide and the bottom is narrow, and the wall surface has been carefully smoothed, presenting a flat and complete right-angled triangle plane. The second type is concentrated in the Bingzhou area, represented by the Northern Dynasties mural tomb in Jiuyuangang, Xinzhou, Shanxi and the tomb of Lou Rui, King of Dong'an in the first year of Wuping in the Northern Qi Dynasty in Taiyuan, Shanxi. The walls of the tomb passage are in the shape of 1-3 shallow steps from top to bottom, and the width of each step is between 0.08 and 0.25 meters. From this, we can further discover that different tomb passage wall shapes do give rise to different decorative appearances.

We can see from the first type of tombs that since both walls of the tomb passage are long triangular planes that are completely connected from top to bottom and from left to right, the planning and layout of the tomb passage murals also have a single level and logic. For example, in the relatively earliest tomb of Princess Ruru, the two walls of the tomb passage, along the bottom edge of the slope, are first arranged from the inside (north) to the outside with 14 frontal standing ceremonial guards of similar height - until the wall height no longer allows the painting of more figures of the same size; then the remaining triangular wall surfaces outside the ceremonial guards are used to paint the mythical beasts Azure Dragon (east wall) and White Tiger (west wall), and filled with lotus, clouds and other patterns; the empty wall surface above the heads of the ceremonial guards in the north of the tomb passage is supplemented with images of fearful beasts, winged people and phoenixes in the clouds [Figure 5]. It is worth mentioning that above the figures on the north and west walls of Princess Ruru's tomb, there are remnants of the Black Tortoise and White Tiger representing the directions, which further confirms that the Azure Dragon and White Tiger at the south end of the tomb passage should be regarded as symbols of the east and west directions. Therefore, this tomb is the first known example of tomb passage murals. Its main wall is used to depict ceremonial figures, and the design intention of filling the corners and blank spaces with blue dragons, white tigers, winged people, fearful beasts, rare birds, auspicious grasses, lucky flowers, and auspicious clouds is obvious at a glance. Similarly, the Wanzhang Tomb, which may be slightly later in age, although its tomb passage is larger and features more than a hundred ceremonial figures, its basic content and wall layout remain the same as the previous tombs; and the Tomb of Xu Xianxiu of the Northern Qi Dynasty in Jinyang, which is of a slightly lower standard, has its two walls of the tomb passage almost entirely occupied by 86 standing ceremonial guards - only six saddled horses were added among the ceremonial guards in the passageways and the patio, which were not seen in the murals of the first two tomb passages in Yecheng.

Figure 5. Sectional view of the tomb of Princess Ruru of the Eastern Wei Dynasty in Ci County. Reproduced by Li Mingqian and Ding Xiaoman based on the "Brief Report on the Excavation of the Tomb of Princess Ruru of the Eastern Wei Dynasty in Ci County, Hebei" (Cultural Relics, Issue 4, 1984, p. 2) published by Ci County Cultural Center.

In the second type of tombs, due to the stepped shape of the walls of the tomb passage, the murals can only be painted in layers. Among this type of tombs, the earliest one is the Northern Dynasties mural tomb at Jiuyuangang in Xinzhou. The three-level stepped walls on both sides of the tomb passage of Jiuyuangang Tomb are built with adobe bricks, which is an unprecedented reinforcement method and reflects the diversity or local differences in ancient tomb construction technology. The murals in the tomb passage are divided into four layers by three steps on the wall: the first layer depicts fairy birds and fearful beasts, immortals, gods and flowing clouds; the second layer mainly depicts people on saddled horses and scenes of horseback hunting in the mountains; the third and fourth layers, whose combined height corresponds to the corridor entrance at the north end of the tomb passage, both depict images of marching warriors - slightly similar to the ceremonial guard processions that appeared before, except that mountains, rocks and trees are painted as filler in the triangular area where the height is not enough to draw more warrior images. This treatment method also makes these two layers of pictures organically connected with the hunting activities in the mountains on the second layer [Figure 6]. The passageway of Lou Rui's tomb is divided into three layers of murals by two levels of stairs: the first layer depicts riding ceremonial figures and camel and horse merchant teams; the second layer depicts riding ceremonial figures; and the third layer depicts standing ceremonial guards. The murals in the passages of these two tombs focus on scenes of horse riding, hunting, business travel, etc., as well as descriptions of the mountain, forest and wilderness environment, which are not seen in the first type of mural tombs. It can be seen that the themes of expression are enriched and expanded due to the multi-layer division of the wall.

Figure 6 Sectional view of the Northern Dynasties mural tomb at Jiuyuangang, Xinzhou

Of course, the shape and features of the wall are not the only determining factors of the subject matter and form of expression of the mural. Interestingly, the tombs of Lou Rui and Xu Xianxiu, which are located in the same place, are of similar age and have similar owners, but the form and content of the murals in the tomb passages are quite different. It seems that we have to take into account the different cultural interests of the deceased, the Han and the Tibetans, and the flexibility of the individual choices made by the bereaved families. This also means that the murals on the tomb passages of high-level tombs outside Yecheng, in addition to depicting ceremonial scenes corresponding to the status of the tomb owner, can still retain the interests of certain tomb owners or individuals of the bereaved family. This also reflects that the murals on the tomb passages that flourished in Yecheng and Jinyang since the Eastern Wei Dynasty were still in an unstable exploratory stage in the Northern Qi Dynasty and had not yet formed a real custom.

Regional Characteristics and Origins of Mural Decorations in Tomb Passages of Western Wei and Northern Zhou

In sharp contrast to the aforementioned tomb examples in the eastern region, the large and medium-sized tombs of the Western Wei and Northern Zhou dynasties in the Guanzhong region in the west generally have passages built with tunnels and patios, and their shapes are quite consistent: the passage is usually more than 30 meters long, consisting of an open, long sloping passage and tunnels and patios spaced apart by archways. There are mostly 3-6 groups of tunnels and patios, which obviously have formed a certain standard. According to the excavation report, there are about 30 tombs from the Western Wei and Northern Zhou dynasties with painted murals or remaining traces of murals, including 21 with murals painted in the tomb passages. It can be seen that decorating tomb passages had become a trend in the Guanzhong region during this period, but its artistic characteristics were completely different from those seen in the eastern region.

First, the wide parallel red bands painted continuously on the upper and bottom parts of the wall extend from the tomb passage to the tomb chamber, forming a border-like decoration. This feature runs through almost all the mural tombs of the entire Northern Zhou Dynasty, which is an extremely significant phenomenon. Regarding the nature of this type of red stripes, based on the brackets painted on the top of similar red wide bands found in the tomb of Yuwen Tong, Duke of Ji, in Xianyang, Shaanxi Province in the sixth year of Tianhe in the Northern Zhou Dynasty (571), it can be determined that it is a symbolic representation of wooden structures such as lintels and pillars. Secondly, what is more striking is that above the passageways of the tomb of Chi Luoxie in the fourth year of Jiande (575) of the Northern Zhou Dynasty in Xianyang, Shaanxi, and the joint tomb of Li Xian and Wu Hui in the fourth year of Tianhe (575) of the Northern Zhou Dynasty in Guyuan, Ningxia, there are painted images of imitation wooden gatehouses. This type of gatehouse image, together with the shadow-shaped wooden structure symbolized by the wide red band, forms a coherent and unified image logic, and together constructs the architectural imagery inside the tomb. Furthermore, as can be seen from archaeological discoveries such as the tomb of Yuwen Tong in the sixth year of Tianhe period of the Northern Zhou Dynasty in Xianyang, the tomb of Anjia in the first year of Daxiang (579), and the tomb of Chiluoxie in the fourth year of Jiande, the tomb No. 11 of the Western Wei and Northern Zhou Dynasty in Xizhaoyu Village, Chang'an District, Xi'an City, the tomb of Yuwen Meng in the fifth year of Baoding period of the Northern Zhou Dynasty (565) in Guyuan, and the tomb of Li Xian and his wife, it is common for tombs in the western region at that time to have 1-2 frontal standing statues of men holding ceremonial swords painted on the east and west walls of the tomb passage (some including both sides of the outer facade of the first passage). This type of mural expression is quite different from the examples seen in the eastern region mentioned above, and is obviously a regional characteristic that cannot be ignored [Figure 7].

Figure 7: Plan and section view of Tomb No. 11 of the Western Wei and Northern Zhou Dynasty in Chang'an, Xi'an

There has been a certain amount of accumulation and progress in the research on the artistic origins of Northern Zhou tomb murals. The recent discovery of a considerable number of tombs from the Sixteen Kingdoms in the Guanzhong region has revealed in a more systematic and intuitive way that the decorative strategy based on multiple groups of tunnel-patio passage structures should be the direct source of the Northern Zhou tomb passage murals. The large tombs of the Sixteen Kingdoms in the Guanzhong region began to have more than one set of passageways and skylights, and the earth platform above the passageways was carved into a decorative method to imitate wooden gatehouses. The gatehouse was usually three bays wide, with a carved door in the middle and straight lattice windows on both sides. Under the eaves were carved brackets, eaves beams and other architectural components [Figure 8]. Its appearance and structure were exactly the same as the gatehouse murals above the arch on the south side of the passageway in the Northern Zhou Dynasty [Figure 9]. Some tombs also had carved column bases and square corner columns at the four corners of the tomb chamber, which complemented the gatehouse above the passageway and formed a harmonious and unified architectural image. It is known that the wooden structure decoration system of the tomb passage in the Northern Zhou Dynasty mural tombs has its origins. Moreover, the warrior images depicted in the tomb passages of the Northern Zhou Dynasty mural tombs had already appeared in tombs during the Sixteen Kingdoms period: for example, the images of ceremonial figures in the tomb chamber of Tomb No. 25 of the Sixteen Kingdoms in Jiao Village, Xi'an, Shaanxi; and the images of warriors holding halberds that remain on the north wall of the front chamber of Tomb No. 298 of the Sixteen Kingdoms in Beihe Village, Xianyang, Shaanxi. Given that the geographical distribution of the Northern Zhou mural tombs is highly overlapping with that of the Sixteen Kingdoms mural tombs, it is undoubtedly more logical for their decorative themes to directly inherit local painting patterns than to adopt Hexi or southern powder models.

Figure 8: Plan view and section view of the Sixteen Kingdoms Tombs in Chang'an, Xi'an

Figure 9 Image of the gatehouse above the first passage of the tomb of Li Xian and his wife of the Northern Zhou Dynasty in Guyuan

Compared with the tall, continuous walls of open tomb passages in eastern China, the sizes of walls available for painting in Northern Zhou tomb passages vary greatly because the passages and patios are often staggered at short distances and the walls at the passages are much lower and narrower than those at the patios. Limited by these conditions, it is difficult to depict a large ceremonial procession of large numbers of people of equal stature and continuous and uninterrupted length on both sides of the tomb passage in this type of tomb. Instead, only 1-2 pairs of ceremonial guards standing facing each other can be drawn based on the height and width of the walls of the patio and the passage. Taking the tomb of Li Xian and his wife as an example, the passageways of the tombs all have arches at a height of 1.45 meters, and the top of the arches is 1.55-1.6 meters high, which can barely allow people to pass through. Therefore, the height of the portraits painted on the walls is only about 1.4 meters. The skylight leads directly to the ground, and there is a significant difference in height with the walls of the passageways, so the height of the portraits painted on the walls can be over 1.6 meters. In this way, the representation of paired single ceremonial guards in response to each spatial unit formed by a patio and a passageway became a basic element of the regional characteristics of the murals in the tomb passages of the Northern Zhou Dynasty tombs.

The ambiguity of spatial cognition in the early stage of tomb passage murals

The mural tombs of the Eastern Wei and Northern Qi dynasties were in the initial stage of the development of tomb passage murals from scratch, so overall, a relatively stable spatial logic between the tomb passage and the burial chamber had not yet been clearly established. However, the best way to understand the specific spatial expression intentions of the tomb passage decorations at that time is to compare them with the contents of the tomb chamber murals.

The murals in the Wanzhang Tomb are not well preserved, but the scenes painted inside the tomb can still be seen in Princess Ruru's tomb: with the image of the tomb owner in the middle of the north wall as the center, it is surrounded by female attendants holding curved lids and fans, and extending to the east and west walls of the tomb. In other words, unlike the male ceremonial figures on the two walls of the tomb passage, the servants painted in the tomb chamber of Princess Ruru are mainly female, which obviously shows the indoor service activities centered on the tomb owner. However, the "inner service" and "outer ceremonial" arrangements in Princess Ruru's tomb, that is, the murals with the tomb gate as the boundary, with different interior and exterior areas, were not fully continued. At the end of the Northern Qi Dynasty, the tomb of Gao Run, the fourteenth son of Gao Huan and King Wen Zhao, which was also of extremely high standards in the first year of Longhua (576), has paintings on the east wall of the tomb chamber with scenes of people holding umbrellas and chariots. The subject matter and position arrangement are very similar to those of the Northern Qi mural tombs of Xu Xianxiu, Lou Rui, and Taiyuan No. 1 Thermal Power Plant, which are of similar age. The murals in Xu Xianxiu's tomb no longer use the tomb gate as the boundary to divide the areas for attendants and ceremonial guards. The northern section of the east and west walls of the tomb chamber are painted with chariots and horses, while the southern section begins to feature a procession of ceremonial figures wearing turbans and long gowns with narrow sleeves. This procession continues to the southernmost end of the two walls of the tomb passage without being interrupted by the passageway and patio in the middle (Figure 10). This shows that the murals in the tomb passage of Xu Xianxiu's tomb can still be regarded as an extension or extension of the tomb chamber murals.

Figure 10 Sectional view of the tomb of Xu Xianxiu of the Northern Qi Dynasty in Taiyuan

This blurred boundary between the tomb passage and the tomb chamber is also reflected in the painter's use of specific ceremonial characters. Take the Northern Qi mural tomb in Shuiquanliang, Shuozhou, Shanxi as an example. The tomb is a brick chamber tomb with a long sloping passage, but the paintings are only applied in the corridor and the tomb chamber. The southern section of the east and west walls of the tomb chamber are painted with 1-2 groups of smaller-sized figures of ceremonial guards on horseback and holding flags in the distance [Figure 11], which are quite consistent with the figures of ceremonial guards on horseback and holding flags on the second layer of the east and west walls of the tomb passage of Lou Rui's tomb [Figure 12]. In addition, on both sides of the tomb door, there are two people standing opposite each other playing long horns (Figure 13), and the same images are distributed on both walls of the tomb passages of Xu Xianxiu's tomb and Lou Rui's tomb (Figure 14). This phenomenon can be understood as follows: when there is no decoration on the tomb passage, the tomb chamber murals can incorporate some elements of the tomb passage murals. In other words, in the collective consciousness of painters at that time, there was no distinction between the two different burial spaces, the tomb chamber and the tomb passage, and there was no need to deliberately distinguish them when processing the murals.

Figure 11: Image of a riding figure on the east wall of the Northern Qi mural tomb in Shuiquanliang, Shuozhou (partial)

Figure 12: Image of a riding figure on the second layer of the west wall of the tomb passage of Lou Rui of the Northern Qi Dynasty in Taiyuan (partial)

Figure 13: The image of a drummer on the south wall of the Northern Qi mural tomb in Shuiquanliang, Shuozhou

Figure 14: The third layer of the eastern wall of the tomb passage of Lou Rui of the Northern Qi Dynasty in Taiyuan

Unlike the eastern region, the configuration of murals in the Northern Zhou mural tombs, such as the gate tower images stably distributed above the passage, and the human figures mainly painted on the patio and the walls of the passage, reflects the clear correspondence between the images and the architectural structure, indicating that the painters did have different understandings and imaginations of different areas of the tomb passage. But it is undeniable that this awareness is immature and still in its infancy. Taking the gate tower diagram as an example, although in terms of spatial position, it is part of the image program of the passage and patio area, when combined with the overall tomb murals, it may belong to the same decorative system as the shadow-made wooden structure symbols. This also means that although the murals in the tomb passages of the Northern Zhou Dynasty have begun to distinguish spaces in visual expression, this seems to be only a temporary technical strategy to cope with the changes in the shape of the tomb passages, and is far from forming a complete set of tomb passage decoration concepts with clear intentions and stable content.

3. The themes and actual connotations of the two traditions of tomb passage murals

By examining the relationship between the tomb passage form and the tomb passage murals through archaeological materials, we can find that tomb murals are likely to lag behind the changes in the tomb shape, and it takes a period of adjustment to develop a decorative system that is compatible with it. The reason why the grand and long tomb passage space had already been formed in the Western Jin Dynasty, but the tomb passage murals only came into being in the late Northern Dynasties, in addition to being restricted by the wall shape, is also because the content of the murals that were commonly painted in tombs before was difficult to apply to the narrow and long tomb passage, and it took some time to explore the decorative themes suitable for the tomb passage.

Identifying identity: Rethinking the theme of "Lu Bu" in the murals of tomb passages in the eastern region

Regarding the large ceremonial processions in the murals of the Eastern Wei and Northern Qi tomb passages in the Yecheng area, Zhao Yonghong determined that their nature was a procession, but he did not compare the ceremonial procession images with the specific records in the literature. Yang Zhishui filled this gap and believed that the ritual utensils in the Wanzhang Tomb "are mostly consistent with the emperor's procession, and many of them can show their origins and changes." The work of the above two scholars represents the basic understanding of the current academic community. However, their research did not carefully examine other mural tombs of the same period and ignored the key image of the chariot.

What is Lu Bu? Cai Yong explained in "Duduan" that "when the emperor goes out, the order of the carriages is called Lubu, which includes the big carriage, the formal carriage, and the small carriage." It can be seen that the Lubu ceremony was centered on the carriages from the beginning. Relevant documents from the Han and Wei dynasties show that in addition to the chariot and its decorations, the procession also included the ceremonial guards in front and behind. As recorded in "Fengshi Wenjianji", "When the emperor travels on a royal journey, the entourage of feathered guards is called Lubu, and the name has only been used since the Qin and Han dynasties." Therefore, the graphic representation of Lubu should also focus on the carriage that the host rides, supplemented by the ceremonial guards in front and behind.

In fact, similar procession scenes are indeed depicted in tomb images from the Eastern Jin Dynasty to the Northern Wei Dynasty. The earliest one is the mural Tomb No. 3 in Anyue in the Korean Peninsula in the 13th year of Yonghe in the Eastern Jin Dynasty (357) [Figure 15]. Later, it was also seen in the Northern Wei tomb murals and coffin board paintings in the Pingcheng area. The characters in these images are arranged in a square formation, with guides and drums in front, infantry and cavalry surrounding the outside, and mounted guards or attendants following behind. Elements of acrobatics were added during the Northern Wei Dynasty, but the chariot is clearly the center of the picture.

Figure 15. Ceremonial images on the east wall of the rear chamber and corridor of the No. 3 mural tomb of the Eastern Jin Dynasty in Anyue, Korean Peninsula

However, this is not the case with the ceremonial images in the mural tombs of the Eastern Wei and Northern Qi dynasties. The Wanzhang Northern Dynasties mural tomb is the highest-specification one known so far of this period. In addition, it is relatively early in age and should be an important reference for the mural tombs of the same period. There are 53 people painted symmetrically on the east and west walls of the tomb passage. Each of them holds a weapon (including fork, spear, sword, knife, shield, banner, drum, cloak, umbrella, fan, xiangfeng, canopy, cover, banner, festival, flag, banner, halberd, halberd, etc.), and they are arranged in sequence from south to north. In other Eastern Wei and Northern Qi mural tombs, the most common depictions are of people holding flags and long horns, and the complete and complex ceremonial configurations are no longer reproduced. For example, the passage of Princess Ruru's tomb is painted with seven ceremonial guards holding ceremonial swords or flags, six ceremonial guards standing under rows of halberds, and one gatekeeper from south to north; the tomb of Gao Xiaoxu, King Xiucheng of the Northern Qi Dynasty, whose age is unknown, has 13 standing ceremonial guards symmetrically painted on both walls of the passage, holding long horns, ceremonial swords, and flags. The content and scale of the ceremonial guards are similar to those painted in Princess Ruru's tomb; the number of ceremonial guards in the murals of Xu Xianxiu's tomb has increased significantly, including not only those holding long horns and flags, but also a considerable number of those holding swords and weapons and standing with their hands folded; while in Lou Rui's tomb, only the third layer of the passage is painted with ceremonial guards holding long horns, flags, and standing with their hands folded, while the first and second layers are painted with large areas of riding figures.

Through the investigation of the ceremonial images in Eastern Wei and Northern Qi tombs, it is not difficult to find that the most core images of the chariot in the procession do not appear in the murals in the tomb passages. It is true that saddled horses and ox carts appeared in the later tombs of Gao Run, Xu Xianxiu and Lou Rui, but they were painted on the east and west walls of the tomb chamber respectively, far away from the center of the north wall where the tomb owner's portrait was located. Although they were the chariots and mounts of the tomb owner and his wife, such ordinary chariots and mounts did not necessarily have ritual significance that could reflect one's social status. In addition, judging from the current status of the remaining murals in the tomb chambers of the Northern Dynasties mural tombs in Wanzhang, there were no chariots and horses in the highest-level tomb decorations at that time; there were no images of chariots and horses in the earlier tomb of Princess Ruru, which means that chariots were not the focus of ceremonial images in the Eastern Wei and Northern Qi dynasties. Compared with the core connotation of the traditional Lubu in the Central Plains, this is quite different.

Moreover, some of the tomb passage murals also contain images of rows of spears, which are not part of the procession but also have hierarchical significance. The tomb of Princess Ruru and the Northern Dynasties mural tomb in Wanzhang depict two rows of halberd racks in detail at the north end of the tomb passage near the tomb chamber, with twelve and ten halberds inserted respectively, and ceremonial guards behind the racks [Figure 16]. According to Yang Hong's analysis, the halberds lined up in front of the door may have originated from the lancets that were often placed in front of the doors of nobles in the Han Dynasty. At the latest, they had appeared in front of the mansions of high-ranking officials in the late Northern Dynasties. For example, "Book of Zhou·Biography of Da Xi Wu" says: "(Wu) when he held an important position, he did not show his dignity, and usually rode alone, with only one or two people on his left and right. No halberds were used at the outer gate, and the door was always closed during the day." A mature door halberd system was formally formed during the Sui and Tang dynasties. "Six Codes of Tang" and "New Book of Tang·Biographies of Officials" and other documents all have detailed regulations on the specific use of door halberds, especially the number of halberds and the rank and identity of their corresponding owners. From this perspective, the images of rows of halberds in the tomb passages of the Eastern Wei and Northern Qi dynasties should have dual meanings: one is at the hierarchical level, intended to highlight the noble status of the tomb owner during his lifetime or to demonstrate his power; the other is at the spatial level, intended to imply that the location of the ceremonial guard is right in front of the door of the tomb owner's underground residence.

Figure 16. The image of the ceremonial guards on the north end of the east wall of the tomb passage of the Northern Dynasties mural tomb in Wanzhang, Ci County

Compared with the contents of the murals in the tomb passages of the above-mentioned Northern Dynasties, the contents of the murals in the tomb passages of the Jiuyuangang Tomb in Xinzhou are quite different. Not only is there no trace of the so-called "Lu Bu", it is even difficult to identify any traces of "ceremonial guards". The southern section of the second layer on the east and west walls of the tomb passage depicts a scene of multiple groups of people talking to each other around saddled horses, and there are also images of Hu people among them; the northern section depicts horseback riders holding spears or bows and arrows hunting wild beasts in the mountains and forests; and the marching warriors painted in the southern sections of the third and fourth layers do not hold any ceremonial instruments. Not only are their attire exactly the same as the horseback hunters in the previous layer, but they are also located in the middle of a series of mountains, as if intentionally emphasizing their possible connection with the hunting team [Figure 17]. Obviously, this kind of content does not fall into the category of ceremonial guards, but similar expressions of hunting in the mountains and forests are often seen in tomb decorations with strong Xianbei characteristics during the Pingcheng period of the Northern Wei Dynasty. The reason for this may be due to the hunting culture that is commonly loved by nomadic peoples. Coincidentally, Lou Rui's tomb also contains some mural themes that are rarely seen in Han tombs, such as the marching camels and Hu people painted in the southern section of the first layer of the tomb passage, which looks like a picture of long-distance trade, as well as the wild natural environment expressed by images of trees in the tomb passage, corridors and even the tomb chamber. The owners of these two mural tombs were probably not Han people. The diverse themes of the murals in their tomb passages more often show the cultural identification with nomadic peoples outside the ritual system of Han culture in the capital.

Figure 17 Mural on the east wall of the Northern Dynasty Mural Tomb at Jiuyuangang, Xinzhou (partial)

In short, gathering the above information, it is not difficult to come to the following conclusion: the ceremonial images in the murals of the tomb passages of the Eastern Wei and Northern Qi dynasties are not centered on the chariot, but are integrated with other symbolic elements that can identify hierarchical status and ethnic identity, such as rows of spears and hunting. Therefore, it may be a bit far-fetched to define its theme as the procession. It is more likely that some ceremonial categories in the procession were used as a reference for the creation of the mural, in order to highlight the majesty of the tomb owner during his lifetime and the honor he enjoyed after his death. At the same time, the complexity and diversity of the themes of the tomb passage murals of this period, as well as their inherent cultural orientation, should not be ignored.

Guarding the Gate: The Spatial Imagery of Tomb Passage Murals in Guanzhong Region

As mentioned earlier, in addition to the red parallel strips running through the entire wall of the Northern Zhou tomb passage murals, images of ceremonial guards and gatehouses are distributed in the passageways and patio areas. The combination of space and images involved may be the key to our understanding of the meaning of tomb images. Here, it would be helpful to take a closer look at the image configuration of the Northern Zhou tomb passage murals.

Figure 18: Images of ceremonial guards in the tomb passage of Li Xian and his wife from the Northern Zhou Dynasty in Guyuan

On the north side of the east wall of the fifth patio of Yuwen Meng's tomb, there remains a profile portrait of a man wearing a fu hat, wide-sleeved hakama, and holding a long sword in his hand. The tomb of Li Xian and his wife has a double-story gatehouse painted above the arch on the south side of the first tunnel and the entrance to the corridor, and a single-story gatehouse painted above the arch on the south side of the third and fourth tunnels. The south edges of the tunnels are all painted with red borders. On the east and west sides of the south of the first tunnel, there is a man wearing a crown and a robe and holding a long sword. There is a warrior painted on each of the east and west walls of each tunnel, and two warriors painted on each of the east and west walls of each patio, a total of 18 warriors, all wearing wide-sleeved hakama, pleated crotch and Mingguang costumes, holding long swords on their shoulders (Figure 18). The southern edges of each passageway in Tomb No. 11 of the Western Wei and Northern Zhou Dynasty in Xizhaoyu Village, Chang'an District, are painted with red borders. On the east and west sides of the south side of the first passageway and on the north sides of the east and west walls of the first and second patios, there should be a painting of a warrior wearing a tall crown, a cross-collared and wide-sleeved robe, and holding a long sword (three are still there). There are painted gatehouses above the arches on the south side of each passage entrance to Chi Luoxie's tomb, and red wide band patterns are painted on the south edge of the passage. A half-length human figure remains in the middle of the east wall of the sixth passage. On the north side of the east and west walls of the third and fourth patios of Anjia's tomb, there are remains of a frontal image of a man wearing a helmet, armor, and holding a sword in both hands [Figure 19].

Figure 19: Plan and section drawings of the Anjia Tomb of the Northern Zhou Dynasty in Xi'an

From the above information, we can know that during the Northern Zhou Dynasty, although the ceremonial guards of some tombs (such as the tomb of Li Xian and his wife) were evenly distributed on both walls of the tomb passage, and the overall appearance seemed more like a ceremonial performance, the more common situation was to paint standing statues of warriors with swords on both sides of the outer facade of the first tunnel (i.e. the south entrance) or on the north side of the east and west walls of the patio close to the tunnel. The regular position of the image of the warrior with a sword intuitively reveals the close connection between the ceremonial guards and the passage. Due to mechanical requirements, the passageways in Northern Zhou tombs are usually arched earthen cave structures. Because the tunnel has a certain depth, in order to facilitate passage, the height from the top of the arch to the ground is generally around 2 meters. This easily reminds people of the doorway structure of ground buildings with very similar functions and appearance. The red strip decorations on the edge of the exterior facade of the Northern Zhou tomb passage and the gatehouse image painted above it not only show the special attention paid to the passage area, but also fully confirm that the tomb builders had endowed the passage with the imagination of a "door". In this way, the spatial image expressed by the image combination of "one gate and two ceremonial guards" - the solemn image of pairs of ceremonial guards guarding the heavy gate - also appears faintly before our eyes.

Another basis for defining the figures in the Northern Zhou tomb passage murals as gate guards lies in the consistent characteristics and positions of such images in tombs of previous dynasties and other regions. As mentioned above, regardless of how the clothing of this type of male standing statue changes, they all either lean on or hold a straight long sword that is more than half a person's height. Similar standing statues with swords were popular in high-level tombs of the Southern Dynasties, such as the Southern Dynasties mural tombs in Wujia Village, Huqiao, Danyang, Jiangsu, the Southern Dynasties mural tombs in Jinjia Village, Jianshan [Figure 20], and the Southern Dynasties mural tombs in Xuezhuang, Deng County, Henan. In all of them, a pair of figures with swords were symmetrically arranged on both sides of the tomb door or corridor. After entering the Northern Qi Dynasty, first there was the Northern Dynasties mural tomb in Wanzhang, which painted four ceremonial guards with swords behind the halberd rack at the north end of the tomb passage near the tomb chamber, and later there were two men with swords painted on both sides of the tomb door of Lou Rui's tomb. The above archaeological materials show that, over the past hundred years, although the pattern of this type of standing statue with a sword has circulated and developed among different regional cultural traditions, its position has not changed significantly and has always been distributed around the tomb gate. This profoundly reveals its visual significance as a "gatekeeper". The Northern Zhou tombs moved the sword-wielding ceremonial guards who were usually located near the tomb gate to the tomb passage area and combined them with the gatehouse images above the multiple passages. This practice can be seen as a clever use of the previous gate guard pattern that is neither contrary to tradition nor unconventional.

Figure 20: Images of ceremonial guards on the east and west walls of the corridor of the Southern Dynasties brick tomb at Jianshan, Danyang

Based on the above, we can draw the following conclusions:

First, since the Wei and Jin Dynasties, the construction of multi-layer stepped tomb passages and through-hole-patio tomb passages in high-level tombs had no direct connection with the social status of the tomb owner. In nature, they belonged to two different tomb passage construction technologies, which were used to overcome the risk of collapse brought about by the increasing scale of tomb passages. Since the tunnel-patio-style tomb passage was more scientific, labor-saving and more suitable for painting murals, the stepped tomb passage was completely replaced during the Sui and Tang dynasties.

Second, at the end of the Northern Dynasties, the eastern region centered on Yecheng and the Guanzhong region centered on Chang'an explored their own different modes of tomb passage mural decoration based on the different tomb passage forms formed by different construction techniques: the tomb passage murals in the eastern region took ceremonial figures as the basic theme, and arranged the figures from the inside (north) to the outside along the two walls of the tomb passage, and expanded the relevant expressive themes according to the wall conditions; the tomb passage murals in the Guanzhong region continued the tradition of shadow-made wooden structure decoration in the tombs of the Sixteen Kingdoms, and combined with the spatial form of the passage, created an image combination of "one gate and two ceremonial guards", and constructed a spatial image of "guarding the double gates".

Third, compared with the relatively consistent visual expressions of the mural tombs of the Western Wei and Northern Zhou dynasties in the Guanzhong region, the mural tombs of the Eastern Wei and Northern Qi dynasties in the eastern region have richer themes, far beyond what can be covered by the "Lu Bu". They also include images of rows of halberds that have the dual meanings of identifying identity and defining space, as well as the different cultural interests of the tomb owners, namely the Han and Tibetan peoples. Moreover, various signs show that the tomb passage murals in the Guanzhong region had already formed certain norms during the Northern Zhou Dynasty; while the tomb passage murals in the eastern region (especially the Bingzhou area) had not yet formed a real custom until the Northern Qi Dynasty.

In short, the tombs of the late Northern Dynasties underwent a significant change from non-existence to the presence of murals in the tomb passages. Only by examining this process from a technical perspective can we reveal the design intent and planning ideas of tomb art, and then understand the causes of the two regional traditions of tomb passage murals in the northern region. The high-level tombs of the Sui and Tang dynasties integrated the above decorative traditions and developed the tomb passage murals to their peak. Therefore, clarifying the organic interaction between architecture and images in the Northern Dynasties tomb passage murals is the important foundation for our understanding of the construction and decoration of Sui and Tang tomb passages.

(The original title of this article is "Negotiation between Technology and Art: On the Origin of Two Regional Decorative Traditions in Northern Dynasties Tomb Passage Murals", published in the Journal of the Palace Museum, Issue 3, 2025. The Paper is authorized to publish this article by the author.)