Tiananmen Square was originally designed and built in 1651. It was enlarged to four times its original size and cemented over in 1958; it covers an area of 40.5 hectares (100 acres), and each flagstone is numbered for ease in assembly of parades. The square derives its name from the massive stone Tiananmen (“Gate of Heavenly Peace”; first constructed in 1417)—once the main gate of the former Imperial Palace—situated at its northern end. In the centre of the square, on a two-tiered marble terrace, is the Monument to the People's Heroes (completed 1958). A monumental museum complex (opened 1961) lying to the east of the square includes the Museum of the Chinese Revolution (dedicated to Chinese history since 1919) and the Museum of Chinese History (dedicated to Chinese history before 1919). To the south of the Monument to the People's Heroes is the Mao Zedong Memorial Hall (completed 1977), in which the body of Mao lies in state. Farther south is the Front Gate, constructed during the reign (1402–24) of the Ming-period Yongle emperor. Lying on the western side of the square is the Great Hall of the People (completed 1959). It is the site of the annual meetings of the National People's Congress and contains a meeting hall with more than 10,000 seats and a banquet hall capable of seating 5,000.