Like many of Chinas ancient cities Nanjing was once a walled city. The walled city featured sever gates but the south gate is quite special for a number of reasons. One visible reason is that it looks more like a castle than a gate.
It took over 20 years to build beginning in 1366 and features an entry with four arched doorways, three internal courtyards, storage tunnels and wide ramps either side of the courtyards leading to the top of the wall.
It remains standing today some say due to the high importance placed on quality of construction, if you look closely at the walls bricks you can still see the individual markings on the bricks identifying the bricks maker.