Zhonghua Gate, meaning Chinese gate, was the biggest and most splendid city gate of the Nanjing city wall in the Ming dynasty(1368-1644). 
The gate was built from 1366 to 1386 and originally named Gate of Gathering Treasure, since legend says in the construction, the wall collapsed again and again until a "Box of Gathering Treasure" was buried under it. The whole structure was built with huge bricks and special cement made from lime, tung oil and sticky rice juice, and was extraordinarily strong.
The delicately designed gate has four archways, and three "trap cities" which are enclosed spaces between the archways. On the gate there are 27 hiding caves where more than 3,000 soldiers could ambush enemies in wartime. The biggest one is 44.34 meters high, 6.84 meters wide. Every archway has a wooden gate, and an additional iron gate which would be lowered in case the wooden one was broken through. Enemy soldiers caught in the "trap city" would be ambushed with ease. On the top of the tower there used to be a watchtower as well as other structures.
Information From:china-travel-agent.com
