A line of fortifications extending about 2,414 km (1,500 mi) across northern China. Built in the third century by some 300,000 laborers (mainly criminals, conscript soldiers, and slaves), the wall proved ineffective against invaders and is today a major tourist attraction. a large strong wall that was built across northern China during the third century BC to protect the country against enemy armies. It is over 2000 kilometres long. 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