China’s earliest drainage system unearthed

The earliest urban water drainage system in China has been discovered in the ancient city of Pingliangtai in the Huaiyang District of Zhoukou City, central China. The ceramic water pipes are 4,000 years old, dating to the Chinese Neolithic Longshan period.

The Neolithic settlement of Pingliangtai had a population of about 500 people and was enclosed by earthen walls surrounded by a moat. It was on a river plain and subject to seasonal monsoons that flooded the city in a flash. Figuring out how to drain accumulated water outside the walls was essential to the city’s survival. The excavation has revealed an extensive and well-designed urban drainage system running along roads, through the earthen walls and city gates.

To help mitigate the excessive rainwater during the rainy seasons, the people of Pingliangtai built and operated a two-tier drainage system that was unlike any other seen at the time. They built simple but coordinated lines of drainage ditches that ran parallel to their rows of houses in order to divert water from the residential area to a series of ceramic water pipes that carried the water into the surrounding moat, and away from the village.

One set of pottery pipes in excellent condition were found under the pavement in the guardhouse of the South Gate, passing through the city walls. They were set in a ditch dug at a slight incline (high inside the city walls, low outside), wide at the top and narrow at the bottom. Two pottery water pipes of the same dimensions and diameter were laid side-by-side at the bottom of the ditch. They were then buried and paved over by the road leading in and out of the gate.

Another set of pipes were found to have been installed through a break in the city wall. This was likely an emergency measure to drain the city after a flood event. After the water was drained, the gaps in the city wall were repaired and the pipes laid in ditches for permanent drainage.

The ceramic pipes are straight tubes in segments about 14-18 inches long. The sections interconnected to extend the length of the pipes and transport the water over long distances. The thickness of the pipe walls are consistent, as is the pattern on the surface, indicating they were a standardized product built specifically for the municipal drainage system. It could not have been ad hoc, laid down by neighborhoods or individual property owners; this was a designed and executed example of urban planning by the community, not a powerful central state authority.

What’s surprising to researchers is that the settlement of Pingliangtai shows little evidence of social hierarchy. Its houses were uniformly small and show no signs of social stratification or significant inequality among the population. Excavations at the town’s cemetery likewise found no evidence of a social hierarchy in burials, a marked difference from excavations at other nearby towns of the same era.

But, despite the apparent lack of a centralized authority, the town’s population came together and undertook the careful coordination needed to produce the ceramic pipes, plan their layout, install and maintain them, a project which likely took a great deal of effort from much of the community.

The level of complexity associated with these pipes refutes an earlier understanding in archaeological fields that holds that only a centralized state power with governing elites would be able to muster the organization and resources to build a complex water management system.