Xian City Wall
The city wall of Xi'an is an extension of the prior Tang Dynasty structure. It was stared in 1370 and finished in 1378 and has a rectangular–shaped construction. It is over 4 kilometers from the east to west and about 3 kilometers from the north to south. And the total length is 13.7 kilometers. It stands 12 meters high, 12-14 meters wide across the top and 15-18 meters thick at the button. On the top of the city wall, there is a rampart every 120 meters, which extends out from the main wall. The top of the rampart is at the same level as the top of the wall. The ramparts were built to allow soldiers to see those enemies who would try to climb up the wall. The distance between every two ramparts is just within the range of arrow shot from either side. This allowed soldiers to protect the entire wall without exposing themselves to the enemy. There are altogether 98 of them on the city wall and each has a sentry building on top of it.
There are four main gates of the city wall on each side-named the east gate, the west gate, south gate and north gate. The four gates of the city wall were the only way to go into and out of town. A watch tower is located on each of the four corners of the wall. The one at the southwestern corner is round, probably after the model of the imperial city wall of the Tang dynasty. But the other three are square and are higher and larger than the sentry building on the ramparts. This shows the strategic importance of the corners of the city wall.