Xi'an is one of the last Chinese cities to have completely preserved its ramparts. 14km in length, they are punctuated by four main gateways recognisable by their monumental towers, and ten secondary gates, five of which are located along the southern section of the walls. Imposing watchtowers stand guard in the four corners. The thickness of the walls is 12m at the top and close to 18m at the base, with a consistent height of 12m.