The evelution of Buddhism in Mongolia can be divided into three distinct periods. Erdene Zuu was the first Buddhist monastery to be built during the third of these in Khalkh Mongolia.
The monastery was founded by Avtai Sain Khan, a descendant of Chinggis Khaan and the great-grandfather of the first Bogd Lama Zanabazar.
According to some sources, the earliest part of the monastery was the Gol Zuu Temple, which was established in summer of 1586 (or, according to the lunar calendar, the 15th day of the middle month of summer in the Fire Dog year).
By 1872 the monastery contained over 500 buildings including 62 temples and housed 1500 monks. Unfortunately the majority of the temples and other buildings were destroyed during the political repression in the 1930s, as happened to monasteries throughout Mongolia.
Erdene Zuu became a state historical religious museum in 1965. It contains 7464 exhibits belongs to XVI-XIX century, including historical and religious objects made of brass, wood carvings, paper-mache, earth-paintings and applique displayed in nine temples. 120 of the exhibits are unique to Mongolia.
Source: Erdene-zuu monastery museum