Andingmen -- literally "Gate of Settled Peace" -- was one of nine gates in the inner wall of Beijing's Ming-dynasty fortifications. Built in the 15th century as part of the defensive system that enclosed the emperor's capital, the gate served a specific function in the city's carefully ordered geography. Each gate had its designated traffic: Andingmen was traditionally the gate through which empty carts returned to the city, complementing Deshengmen to the west, through which military expeditions departed. The walls themselves were massive -- thick enough at the top to drive a carriage along, tall enough to dominate the flat North China Plain for miles. They enclosed a city designed as a physical expression of cosmic order, with the Forbidden City at its center and successive rings of walls marking gradations of sanctity and power.

In the 1950s, the newly established People's Republic faced a decision that still divides historians and architects: what to do with Beijing's ancient walls. The prominent architect Liang Sicheng passionately advocated for preservation, proposing that the wall tops be converted into an elevated public park -- a green ribbon encircling the old city. The government chose differently. The walls were demolished to make way for roads, and most of the gate towers fell with them. Andingmen was torn down along with the others, its stones and bricks repurposed as construction material for the modern city rising in its place. Of Beijing's original nine inner-city gates, only a handful of gate towers survive in any form today. The demolition remains one of the most debated chapters in Chinese urban history.

The 2nd Ring Road that replaced the walls now carries hundreds of thousands of vehicles daily along exactly the path the fortifications once followed. Andingmen Bridge, the roundabout overpass at the gate's former location, links Andingmen Inner Street -- running south into the old walled city -- with Andingmen Outer Street, heading north into what was once open country beyond the walls. The naming convention preserves a distinction that no longer physically exists: there is no wall to be inside or outside of. Beneath the overpass, Andingmen Station on Line 2 of the Beijing Subway follows the same circular route as the vanished walls, its passengers tracing the old fortification plan underground every day without most of them ever knowing it.