Yungang Caves, at Datong City, is one of China's four most famous "Buddhist Caves Art Treasure Houses". They were carved in sandstone from about AD 460 to 470, and are a product of the Northern Wei Dynasty. Still extant today are 53 grottoes and 50,000 statues that include Buddhas, Bodhisattvas, and flying Apsara. The earliest grottoes to be carved are Caves 16 to 20. They were carved by 40,000 workmen over a hundred-year period.