Look down at the stone threshold beneath the archway. The deep, T-shaped grooves carved into the granite base reveal the true purpose of the Tongfei Gate. While the massive brick superstructure and the curved barbican—the “Moon City”—suggest a defense against invading armies, this entrance was engineered to fight a more relentless enemy: the Fei River itself.

Most ancient fortifications rely on height to intimidate; this gate relies on a seal to survive. During the monsoon seasons that historically swelled the Huai and Fei rivers, the city defenders did not man the battlements with arrows. Instead, they engaged a hydraulic defense system designed in the Song Dynasty. They slid heavy wooden planks into these stone channels, packing the gaps with reeds and sticky clay. In hours, the civic entryway transformed into a watertight dam.

This engineering saved Shou County as recently as 1991. When catastrophic floods submerged the surrounding countryside, the Tongfei Gate was sealed, and the city floated like a dry raft in a brown ocean. The water level outside rose nearly to the top of the arch, yet the streets inside remained dry. Standing here, you are not just looking at a military checkpoint, but at the valve of a watertight vessel—a machine that allows the city to coexist with a river that tries, century after century, to swallow it whole.