A line of fortifications across northern China. Originally built during the Qin Dynasty (221–206 bc ) by connecting earlier fortifications, it was subsequently rebuilt and altered many times. The wall reached its greatest extent during the improvements of the Ming Dynasty (1368–1644), when it was expanded to about 6,400 km (4,000 mi) long.
(place, proper) Stone & earth wall extending across N China, built as a defense against invaders in the 3d cent. b.c., with later extensions: 15-30 ft (4.5-9 m) high; 12-20 ft (3.5-6 m) wide; c. 1,500 mi (2,415 km) long.