Tiananmen Square (or the Square of Heavenly Peace) was built in 1651 and has been enlarged several times until it reached its present size, 109 acres (440,500m²) in the 1950s. It’s been the site of several of the most important events in China’s history, including Mao’s declaration of the founding of the People’s Republic of China in 1949, and the protests in the square in 1979 and 1989. The square is named for the Tiananmen Gate, which marks the entrance of the Imperial City, and it also contains other monuments including the National Museum of China and the mausoleum of Chairman Mao.