China: Guard towers on Xian's ancient city wall, by night, Xi'an, Shaanxi Province

Construction of the first city wall of Chang'an (original name of Xi'an) began in 194 BCE and lasted for four years. The existing wall was started during the Ming Dynasty in 1370. It encircles a much smaller city of 14 square kilometres (5.4 sq mi). The wall measures 13.7 kilometres (8.5 mi) in circumference, 12 metres (39 ft) in height, and 15–18 metres (49–59 ft) in thickness at the base. Xi'an is the capital of Shaanxi province, and a sub-provincial city in the People's Republic of China. One of the oldest cities in China, with more than 3,100 years of history, the city was known as Chang'an before the Ming Dynasty. Xi'an is one of the Four Great Ancient Capitals of China, having held that position under several of the most important dynasties in Chinese history, including the Zhou, Qin, Han, Sui, and Tang. Xi'an is the eastern terminus of the Silk Road and home to the Terracotta Army.