Chinese Wanli Changcheng
Defensive wall, northern China.
One of the largest building-construction projects ever carried out, it runs (with all its branches) about 4,000 mi (6,400 km) east to west from the Bo Hai (Gulf of Chihli) to a point deep in Central Asia. Parts of the fortification date from the 4th century BC. In 214 BC Shihuangdi connected existing defensive walls into a single system fortified by watchtowers. These served both to guard the rampart and to communicate with the capital, Xianyang (near modern Xi'an ) by signal
smoke by day and fire by night. Originally constructed partly of masonry and earth, it was faced with brick in its eastern portion. It was rebuilt in later times, especially in the 15th and 16th centuries. The basic wall is about 30 ft (9 m) high, and the towers rise to about 40 ft (12 m). It was designated a UNESCO World Heritage site in 1987.