On July 27, Beijing Central Axis was announced to be inscribed on the UNESCO World Heritage List. In the previous 12 years, there have been a lot of impressive archaeological findings along the Central Axis. Compared to the historical sites in the northern section of the Central Axis like Bell Towers and Wanning Bridge, the relics layout in the southern section is not as clear and comprehensive. In order to restore the complete Central Axis, the Beijing Archaeological Research has worked on its archaeological excavation since 2021.

Through three-year efforts, archaeologists successively identified the location of the historical site of Zhengyang Bridge and excavated the reclic of Tianqiao Bridge, which contributes a clearer layout of the southern Central Axis. These achievements are all recorded in the forthcoming Report on the Archaeological Excavation of Beijing Central Axis (2021-2023).

Recently, the reporter from Beijing Youth Daily interviewed Zhang Lifang, deputy researcher of Beijing Municipal Archaeological Research Institute, who participated in the archaeological excavation, to unveil the stories behind the archaeological work.

Zhengyang Bridge

The Archaeological work of the southern section began with the search for a water-suppressing beast sculpture

“In this archaeological project, our primary task was to find a water-suppressing beast stone sculpture at Zhengyang Bridge,” said Zhang Lifang. In the 1990s, the sculpture from the Ming and Qing Dynasties was discovered near the Zhengyang Bridge site and was reburied for the sake of protection. In August 2021, archaeologists decided to re-excavate it.

The relic of Zhengyang Bridgeis located at the north entrance of Qianmen Dajie (Street), south of the arrow tower of Zhengyangmen. The various limits there made it difficult to carry out large-scale archaeological excavation.

The archaeologists thus reviewed the related excavation archives, hold several rounds of study and discussion, and finally determined the evacuation point. With this point as the center, a 5-meter square working area was delineated.

Thanks to the thorough preparation before, the staff soon unearthed the cement house that protected the sculpture. However, it turned out to be one of the challenges for re-excavation.

“To keep the sculpture intact, we had to demolish this cement house while avoiding that it was damaged by falling steel bars and cement,” Zhang Lifang told the reporter. Archaeologists thus purchased several cotton quilts to wrap the sculpture underground first and then demolished the house outside. As a result, the sculpture was unearthed intact and undamaged.

Reconstructing appearance of Zhengyang Bridge from historical records and ancient paintings

The stone sculpture of water-suppressing beast is an accessory relic of the Bridge. Although the sculpture was found, archaeologists still had no idea about the specific appearance of Zhengyang Bridge in history. Therefore, they conducted on-site excavations while studying historical records.

Fortunately, the images of Zhengyang Bridge were recorded in historical works and paintings from the Ming and Qing Dynasties.

At that time, whenever she had time, Zhang Lifang would visit museums and archives to study the historical records. For the archaeological project, she consulted all the available content about Zhengyang Bridge in compilations of the Ming and Qing Dynasties.

Based on the clues provided by the literature and the construction tradition of ancient bridges, it was assumed that there should be a water-suppressing beast sculpture at each of the four corners of Zhengyang Bridge. “Based on the position and direction of the unearthed one, it was easy to determine that it was the one located at the southeast corner of the bridge,” Zhang Lifang said. As the bridge run north to south, archaeologists continued their exploration towards the northwest and discovered the east facade of the bridge about a meter to the west of this stone sculpture. Northward along the east facade, over half of the east facade of Zhengyang Bridge was excavated

Unraveling the Zhengyang Bridge site from complex clues

According to Zhang Lifang, as Zhengyang Bridge is located on the Central Axis, its north-south axis completely overlaps the Central Axis, and its east-west axis lies in the center of the bridge’s middle arch. As the south embankment and the middle arch were unearthed, the west facade and north boundary were also determined. The four sculpture are symmetrically arranged in pairs. Having identified the position of the one at the southeast corner, the positions of the other three were also confirmed.

The entire excavation process was akin to solving a detective case. In the end, the staff clarified important information such of its specifications and building materials of Zhengyang Bridge through minimal excavation aera, laying the foundation for the subsequent restoration.

Tianqiao Bridge

Archaeological work of the Tianqiao relic conducted section by section

Tianqiao is a bridge located between Zhengyangmen Gate, the main entrance of Beijing’s inner city, and Yongdingmen Gate, that of the outer city. It was often mentioned in historical records from the Ming and Qing Dynasties and deeply embedded in the nostalgic memories of old Beijing people. Excavating the Tianqiao relic is crucial for restoring the southern section of Beijing Central Axis. After multiple rounds of study and dicussion, archaeologists have mostly confirmed that the it is located in the middle of a crossroads. Among the numerous challenges of excavation, the largest lies in the surface of the site.

The site is located in the intersection of Qianmen Dajie (St), Yong'an Lu(Rd), Tiantan Lu(Rd), and Tianqiao Nan Dajie (St South). Surrounded by Tiantan Park, National Natural History Museum, Beijing Tianqiao Performing Arts Center, the place is troubled with heavy traffic and dense crowds.

According to Zhang Lifang, an area of approximately 200 square meters would be needed to excavate the relic as a whole. To avoid disturbing the traffic, the excavation had to be divided into different areas.” For archaeology, the best and most efficient method is to excavate the target as a whole, but the method is not applicable for this case.”

Section-by-section excavations piece together the appearance of the Tianqiao Bridge

Archaeologists could only adopt the method of section-by-section excavation. They divided the working area into three parts, each with limited space. The excavation of each part was accompanied by a traffic diversion. When the work of a part was finished, it would backfilled, and the next section unearthed.

“We can only work in a very small area each time. Therefore, we preserve detailed three-dimensional images for each part and pieced them together to present the overall appearance of the Tianqiao Bridge,” said Zhang Lifang.

However, Tianqiao could be hardly restored as the large-scale infrastructure construction had damaged the upper part of the bridge’s arch. The focus was then put on its lower part. During this process, the staff also discovered the gray-soil foundation and drainage ditches beneath the bridge deck, referred as the “Dragon Beard Ditch” in the works of Lao She, a well-known Chinese writer.

Through excavations, archaeologists confirmed the location of the ditch, clarified its structure, engineering methods in the Qing Dynasty, and discovered the main part of the Bridge built in the Qing Dynasty, outlining the relationship between the ditches, roads, and bridges.

Blue and white porcelain pieces testified the construction date of the Tianqiao Bridge

Regarding the construction date of the Sky Bridge, historical records do not provide a clear account. Based on various evidence gathered by archaeologists, the name of the Tianqiao Bridge first appeared in a complication from Qing Dynasty, proving that the name was adopted before the reign of Yongzheng Emperor. During the Qianlong period, references to Tianqiao appeared sporadically. Hence, the staff preferred the idea the bridge was built during the reign of Qianlong Emperor.

“When sorting the relics, we found that the blue and white porcelain pieces are mainly from the Kangxi and Qianlong periods of the Qing Dynasty,” said Zhang Lifang. The consistence between porcelain pieces and historical records confirms that the excavated parts and associated facilities are indeed remnants of the ancient Tianqiao Bridge.

Expert’s Note

Interpreting the significance of the Beijing Central Axis through archaeological discoveries

Since 2021, in order to deeply explore the historical and cultural significance of the Beijing Central Axis, under the guidance of the Beijing Municipal Administration of Cultural Heritage, Beijing Archaeological Research Institute successively excavated the Zhengyang Bridge site, the road along Central Axis and associated remains, and the Tianqiao Bridge site. The discoveries of roads, drainage ditches and bridges have supplemented the heritage portfolio of the Central Axis, especially its southern section. It provided empirical evidence for the authenticity, integrity, continuity of the Central Axis, vividly reproducing historical scenes in this area.

Design philosophy of the Central Axis

Even numbers represent yin, and odd numbers represent yang. The ancient people used numerical symbols to project the time-space universe. The employment of yang on the Central Axis is manifested in the numbers of buldings, altar layers, and doorways, etc.

Archaeological discoveries also unveil such numerical secrets. The central stone road within Yongdingmen found during August to September 2022 has a width of 4.8 meters, equivalent to one zhang and five chi (zhang and chi are length units in the Qing Dynasty). The middle doorways of the Xiannongmen Gate and Dongtianmen Gate at Temple of Agriculture, serving as the procession routes for state sacrificial ceremonies, also have a width of one zhang and five chi. The width of the drainage ditch under the Tianqiao Bridge is five chi; the width of the bridge body was three zhang and one chi. According to measurements, the distance from Zhengyangmen Gate to the Tianqiao Bridge and that from the Tianqiao Bridge to Yongdingmen Gate are five hundred zhang. Based on the archives, the figure is also true to the length of the stone road from the Tianqiao Bridge to Yongdingmen Gate and the road from Zhengyangqiao Bridge to Tianqiao Bridge. Therefore, these dimensions were not arbitrary but reflected of the ancient thoughts on symbolic number used in designing the sacred space of the imperial city.

Furthermore, five hundred zhang might be a unit length in planning the capital city. For instance, the distances between the Arrow Tower and the Meridian Gate, between the Meridian Gate and the North Gate of Jingshan Mountain, between the North Gate of Jingshan and the Bell Tower are all five hundred zhang. The buildings at the nodes where several five hundred zhang meet are all sacred architectures, dividing the functional areas. The space from the Arrow Tower to the Meridian Gate is the Outer Court; the area from the Meridian Gate to the North Gate of Jingshan Mountain serves as the palace; and that from the North Gate of Jingshan to the Bell Tower represents the market area.

Spatial and ritual order on the central axis

The pedestrian bridge occupies a crucial position on the central axis, serving as a significant spatial and ritual symbol. The location in the middle between Zhengyangmen and Yongdingmen highlights the importance of Tianqiao Bridge, reflecting the meticulous control of the spatial scale and order of the imperial city during its design. Especially during the Qianlong period, two stone steles were erected on the south side of the Tianqiao Bridge, enhancing its impact on the spatial and ceremonial order.

Zhengyang Bridge is another iconic structure on the central axis. Next to Zhengyangmen Gate, which was known as the Gate of the State, the Zhengyang Bridge, located on the moat to its south, holds a significant position. The Bridge, together with the gate tower, arrow tower, and memorial archway, collectively form an interconnected architectural complex, expressing a spatial and ritual order. Among the nine bridges outside the inner city gates, the Zhengyang Bridge stands out as the top in its scale and ceremonial level. During the archaeological work between 2021 to early 2023, a water-suppressing beast sculpture was discovered. Its massive body reaches 3 meters in length, far exceeding the four guardian beasts of the Wanning Bridge, attesting to the position of the Zhengyangqiao Bridge.

The Tianqiao bridge and Zhengyang bridge are distinctive cultural heritages along Beijing’s central axis, representing spatial and ritual order.

Technological innovation in the ancient times

The yulu (the road for the imperial carriage) on the Central Axis is paved with stone slabs on the surface, under which  three-in-one soil is used for foundation. Three-in-one soil is the innovative attempt in building materials and techniques by the people of the Ming and Qing dynasties and was widely used in the official buildings in Beijing in the Qing Dynasty. It is a mixture of loess, sand, and lime strictly blended in certain proportions. A more sophisticated mix may also include sticky rice paste, resulting in a sturdy material even stronger than stone.

Furthermore, the exploration of the sacrificial roads in the Qingsheng Palace of the Temple of Agriculture found that  discovered that the foundation of the Dongtianmen Gate at the inner altar of the Temple of Agriculture, built during the Ming Dynasty, consisted of alternating layers of brick debris and rammed earth. This innovative construction method deviates from the traditional practice of using solely rammed earth for foundations before.

Archaeologists also found brick-lined drainage ditches on the west side of the central-axis road, the bottom of which was reinforced with cypress wood stakes to prevent displacement and settling. According to the archives of the Engineering Administration of the Qing Court, wooden piles were used to reinforce buildings with a soft foundation or near water, for which cypress, cedar, and pine were preferred. Those small and short stakes were referred to as “ground nails.” This ancient practice represents a scientific exploration by the ancients to strengthen building foundations under specific geological conditions.