A researcher cleaning the head of a “water guardian” statue that adorned the central arch of the Zhengyang Bridge Photo: Courtesy of Zhang Lifang 

The Beijing Central Axis first took shape during the Yuan Dynasty (1271–1368), when Beijing served as a capital of Yuan, known as “Dadu.” At that time, the axis of the city extended from the Bell Tower and the Drum Tower in the north to Lizheng Gate, the southern main gate of Dadu. During the early Ming Dynasty (1368–1644), the southern city wall of Dadu was extended southward to the present-day Zhengyang Gate, with the axis extending from Lizheng Gate to Zhengyang Gate. After the construction of the outer city during the reign of Emperor Jiajing (1522–1566), the axis between Zhengyang Gate and Yongding Gate was officially formed. This marked the full extension of the axis from the Bell and Drum towers to Yongding Gate, with a total length of 7.8 kilometers. During the Qing Dynasty (1644–1911), the Jingshan Hill Hall of Imperial Longevity was relocated to the central axis, further refining its spatial structure.

The Central Axis reveals the essence of Beijing’s urban planning and construction, imbued with deep cultural and humanistic significance. It reflects a spatial and ceremonial order that embodies the Chinese philosophy of “upholding righteousness and maintaining balance, and bringing order to the world through proper rites.”

Since 2021, the Beijing Archaeological Research Institute has excavated various sites along the axis, including the remains of Zhengyang Bridge, parts of the central axis road, and the Tianqiao site [lit. heavenly bridge, the essential route for the emperors of the Ming and Qing dynasties to reach the Temple of Heaven for their sacrificial rituals]. Discoveries of roads, drainage systems, and bridges have enriched and completed the heritage elements of the axis, vividly restoring the historical context of this key section.

Design philosophy of the Central Axis

The Records of the Grand Historian states that those who rule the country must value the “three five-hundred-year periods,” [meaning that the rulers of the state must revere the significant transformation cycles of three centuries or one epoch]. In ancient belief, even numbers are associated with yin, and odd numbers with yang. According to the I Ching, Heaven operates through odd numbers to represent yang, and Earth through even numbers to represent yin. This numerical philosophy reflects how ancient people projected their understanding of the universe onto time and space. Since the emperor was considered the “Son of Heaven,” the sacred buildings associated with him often employed yang numbers. Numbers like one, three, five, seven, and nine were frequently used along the Central Axis, as seen in the number of bays in buildings, the layers of altars, and the number of gates.

Archaeological discoveries related to the Central Axis have also uncovered these numerical secrets. In 2022, excavations revealed the historical remains of the central road running from Tianqiao to Yongding Gate, which included seven overlapping roads from different periods, ranging from the Ming Dynasty to the present. The two deepest roads (L6 and L7) date back to the Ming and Qing periods and were part of the Central Axis. L7, the oldest, predated 1729 and was entirely made of compacted soil, with numerous ruts still visible. L6, built in 1729, was a stone road with compacted soil roads on either side, in use until the era of the Republic of China. The soil roads also bear visible ruts. Excavations further uncovered a central stone road built in 1729 within Yongding Gate, measuring 4.8 meters wide—equivalent to 1 zhang and 5 chi in the Qing system of measurement. In the Temple of Agriculture [located near the Temple of Heaven], both the Xianan Gate in the eastern outer wall and the Dongtian Gate in the eastern inner wall, used as ceremonial entrances when the court held sacrificial rituals, also measured 4.8 meters wide, or 1 zhang 5 chi, underscoring the sacred significance of this dimension in the spatial design of the capital.

Excavations at the Tianqiao site from 2022 to early 2023 also revealed similar symbolic numerical applications. The water channel beneath Tianqiao measured 1.6 meters wide, equivalent to 5 chi in the Qing measurement. The bridge itself was 9.98 meters wide, or 3 zhang 1 chi. Strategically located on the central axis between Zhengyang Gate and Yongding Gate during the Ming and Qing dynasties, Tianqiao was 1.6 kilometers (500 zhang) from each gate. Historical records also corroborate that the stone road from Tianqiao to Yongding Gate measured 500 zhang, as did the road between Zhengyang Gate and Tianqiao.

These measurements, such as “1 zhang 5 chi” and “500 zhang,” were not arbitrary. They reflect the symbolic use of numbers in the design of the sacred spaces of the capital, a philosophical expression of the ancient worldview.

Spatial and ceremonial order

Tianqiao occupies an important position along the Central Axis as a crucial spatial and ceremonial symbol. It sits precisely between Zhengyang and Yongding gates, highlighting its centrality on the axis and reflecting the careful spatial order employed in the construction of the capital. During the reign of Emperor Qianlong, two symmetrical stone monuments were placed on each side of Tianqiao, further reinforcing the spatial and ceremonial structure of the Central Axis.

Similarly, Zhengyang Bridge is a key landmark on the axis. Zhengyang Gate was the main southern gate of Beijing’s inner city during the Ming and Qing dynasties, known as the “national gate.” Spanning the moat south the gate, the Zhengyang Bridge was the largest and highest-ranking bridge among the bridges outside the nine major gates of the inner city. Excavations at the Zhengyang Bridge site between 2021 and early 2023 unearthed a “water guardian” statue [usually refers to “Pa Fu,” one of the Nine Sons of the Dragon in Chinese mythology. Believed to be fond of drinking water, Pa Fu often absorbs the floodwaters into its belly when water levels rises nearby. Thus, constructing the statue of Pa Fu by the water embodies the ancients’ wish to prevent floods] from the Ming and Qing periods. The statue, lying on a stone slab on the southern embankment of the river to the east of the bridge, faces southeast with its massive body stretching 3 meters long, demonstrating the high status and grand scale of Zhengyang Bridge.

Ancient technological innovation

The central road built in 1729 exclusively for the emperor, part of the capital’s central axis, featured a stone-paved surface with a foundation made of “sanhe” soil. Sanhe soil, the product of exploration and innovation in building materials and techniques, was widely used for the construction of official buildings during the Ming and Qing dynasties. This carefully blended mixture of loess, sand, and lime, occasionally mixed with glutinous rice paste, produces a remarkably strong material, stronger and more durable than stone, ensuring the stability of structures and preventing distortion due to uneven foundation stress.

During the archaeological excavation of the sacrificial road in the Qing-cheng Hall within the Temple of Agriculture, it was discovered that the foundation of the Dongtian Gate, built in the Ming Dynasty, consists of alternating layers of brick rubble and plain rammed earth. This construction method was also found in the foundation of the Drum Tower during earlier investigations. This architectural foundation structure represents an innovation compared to the long-standing practice of using only plain rammed earth for foundations.

Further archaeological work conducted in 2022 uncovered a brick drainage ditch and a wooden drain on the west side of the central axis road. This brick ditch, reinforced with city bricks and covered with stone slabs, featured cypress wood dowels driven into the earth to prevent deformation and settlement. In the handbook of standard design specifications for official architecture, the Ministry of Works [a government department responsible for overseeing construction, engineering projects, and the management of public works] of the Qing Dynasty recorded that in cases of soft foundations or buildings near water, wooden piles should be used for reinforcement, with cypress, cedar, and red pine being preferred. Short, narrow wooden stakes, known as “ground dowels,” were used to secure foundations, demonstrating the scientific ingenuity of ancient builders in managing challenging geological conditions.

The Beijing Central Axis, with its extensive history and rich cultural heritage, remains a vital source of insights through ongoing exploration and interpretation. Archaeological discoveries continue to deepen our understanding, allowing for a more comprehensive presentation of the axis’s historical value and significance.

Zhang Lifang is an associate research librarian at the Beijing Archaeological Research Institute.