Standing opposite every city gate of old Beijing was an embrasured watchtower, an imposing and distinctive structure that added tremendously to the landscape of the city in old days. Today, only two of them are still there: the Zhengyang Gate and the Desheng Gate.

In days of yore the watchtower was a defence fortification whose tall and sturdy structure, vast vistas and impregnability had won the favour of many an emperor in this country. A typical embrasured watchtower is found in the southeast corner of Beijing. Scooped into its walls are 144 embrasures in four rows.

A barbican entrance was built between a city gate and a watchtower, with a gateway built into either side of the barbican wall to facilitate the traffic of pedestrians, carts and horses. The barbican entrance was an ancillary defence facility that contained a tiny temple and a store selling pots and basins of varying sizes. When the city was under siege, a heavy sluice gate was lowered to close down the city gate, soldiers hidden in the watchtower shot arrows at the enemy, and on the city walls the defenders filled pots and basins with boiling water and poured it at the enemy troops attempting to gain the top of the city wall by scaling ladders. Thus the store selling pots and basins was actually an integral part of the defence system of the city gates.