Beijing’s Central Axis was successfully nominated for World Heritage status. What is the secret behind this axis full of ancient Beijing charm?

Introduction: On July 27, 2024 local time, the 46th World Heritage Conference of UNESCO held in New Delhi, India passed a resolution to include "Beijing Central Axis - a Masterpiece of China's Ideal Capital Order" in the World Heritage List.

(Photo source: People's Daily)

From ancient times to the present, the central axis of Beijing, which runs from north to south, contains the veins of culture, gathers the essence of ancient charm, and demonstrates the unique magnificent order of the capital. In the course of history, it holds up the backbone of the city, touches the years of the ancient capital, and feels the flow and changes of the times.

Ma Quanbao, associate professor of the School of Architecture and Urban Planning at Beijing University of Civil Engineering, believes that the central axis not only has a profound impact on history and culture, but also has driven the superposition of the four values ​​of commerce, transportation, ecology and industry in the old city of Beijing, providing valuable experience and reference for the planning and development of modern Beijing. He said that the wisdom and elegance of Beijing's central axis are enduring and strong. Through its research, we can not only better understand and protect this ancient "backbone of the city", but also draw wisdom from it to guide the planning and construction of future cities. Did you know? On this central axis that embraces nature and contains humanities, there are also some mysteries hidden that you may not have noticed at ordinary times.

The "World's Smallest Castle" on Beijing's Central Axis

Beihai Tuancheng, located on the central axis of Beijing, is known as one of the smallest ancient castles in the world. With a circumference of 276 meters, Tuancheng is an exquisite and unique small garden with colorful cultural relics and monuments. It is also a model of ancient rainwater collection and water-saving projects, and contains many ingenious ideas "from top to bottom". Looking up, the roof of the ancient building in Tuancheng hides a lot of ecological wisdom. It is not difficult to find that the roof is relatively steep above and relatively flat below. The reason for this design is that when it rains heavily, the water above can quickly drain downwards at a larger inclination angle, but when it approaches the eaves, it will gradually flatten, so that the water will rush forward more to prevent rain from damaging the house.

▲The eaves of ancient buildings in Tuancheng At the same time, the ingenious use of tiles also reflects the ancient people's strategy for dealing with rainwater. Wang Chongchen, a professor at Beijing University of Architecture and Civil Engineering, introduced: "The roofs of buildings in Tuancheng are mostly made of staggered tubular tiles and flat tiles. The so-called tubular tiles are arranged with the concave side downward like an arch bridge, while the flat tiles are arranged with the concave side upward, and are mostly staggered. When it rains, water will flow from the tile ridges formed by the tubular tiles to the location of the flat tiles, and then flow along the inclined angle to the end of the flat tiles - the dripper, which has a tip in the middle of the lower part to drain the water, just like when pouring oil, using chopsticks to drain it into a narrow-mouthed bottle to make it flow in a certain direction."

▲Rolled tiles and flat tiles (Photo source: Visual China)

Compared with the use of roof drainage, the design of ground drainage in Tuancheng is more special. Looking down, except for the square bricks and small bricks on the corridor, most areas of Tuancheng are paved with inverted trapezoidal blue bricks. On the one hand, these bricks are permeable bricks, and when raindrops fall to the ground, rainwater can quickly seep in. On the other hand, this inverted trapezoidal arrangement will form a triangular gap between the bricks, making it easier for water to seep into the soil below.

Indeed, even with cleverly arranged permeable bricks as a "weapon for infiltration", when heavy rain comes, it is still possible that the water will not have enough time to infiltrate, resulting in surface runoff. However, there is no need to worry too much. Although there are no drainage outlets and open drainage ditches, these surface runoffs will not cause obvious water accumulation in Tuancheng. When the rain is too heavy, the rainwater will flow down into the culvert along the vertical shaft and be quietly stored for emergency use.

▲The manhole cover

Perhaps few people know that the depths of the bottoms of these shafts are not the same, but fluctuate, which once surprised researchers. "Subsequent research found that the reason for this design is to allow water to stay in it for a longer time, so as to better nourish the plants in this "small castle", especially the large trees with well-developed root systems, so that they can still grow vigorously without external water sources. The reason why we can still see the treasures of Tuancheng today - the ancient Pinus tabulaeformis "Shade Marquis" and the white pine "White Robe General" two historically significant ancient trees are lush and flourishing, which is not without the wisdom of Tuancheng in using water." Wang Chongchen said.

"City Elves" on Beijing's Central Axis

Every April in Beijing, you can often see Beijing swifts flying in and out. So why do they come to Beijing?

▲Flocks of Beijing Swifts (Photo source: Visual China)

In response to this question, Zhao Xinru, associate professor of zoology at Beijing Normal University, explained: "In fact, they who advocate monogamy come to Beijing to build nests and reproduce. The reason they chose Beijing as a breeding ground is because it has many ancient buildings full of historical atmosphere. Whether it is a palace or a temple or an ancient tower, there are often some caves inside, or complex structures such as criss-crossing beams, purlins, and rafters. These are all excellent places for them to build nests. In ecology, they are called nesting niches." Among them, the Temple of Heaven, the Forbidden City, the Temple of Agriculture, the Zhengyangmen and other buildings on the central axis of Beijing are their "favorites".

After choosing a nesting location in an ancient building, the Beijing Swift couple begins to collect materials for nesting during flight. Dry grass leaves, plant stems, feathers, and cotton wool can all become their "building materials." In addition to these materials, they will also pick up some mud, or even some water from a pond, and then mix it with their saliva to gradually build a shallow dish-shaped nest with a concave bottom to better achieve the function of collecting eggs.

▲Swifts in flight (Photo source: Visual China)

"After building the nest, the Beijing swifts will lay eggs in it. They usually only breed one nest a year and lay 2 to 3 eggs. After 21 to 23 days of incubation, the chicks will gradually break out of the shells. When they are just hatched, the chicks have only some sparse down feathers all over their bodies. As the chicks grow older, the down feathers will gradually fade away, and the flight feathers, tail feathers and body feathers will gradually grow out. The young birds will jump out of the nest, spread their wings and fly with the momentum of falling, and welcome their own independent life." Zhao Xinru introduced.

For thousands of years, Beijing Swifts have followed the footsteps of their ancestors, building nests and breeding in Beijing year after year, using this place as their breeding ground. From mid-April to mid-July, they experience the romantic spring and summer of Beijing with us. After completing the important task of breeding, they will embark on a long migration journey to their wintering grounds.

Reporter: Liao Mailun Photographer: Zhang Xinghai (except where noted) Editor: Zhao Ling