Karakorum was the capitol of the Mongol empire in the 13th century. Its name literally means "capital of the world". The ruins of ancient Karakorum are part of the larger World Heritage site of the Orkhon River valley. Stones from the ruins of Karakorum were used in the construction of Erdene Zuu Monastery, begun in 1585 and housing 62 temples by 1872. It is the oldest surviving monastery in Mongolia. The monastery was ruined in 1939 by the Communist purges but the external wall with stupas and three temples remained, becoming museums. In 1990, the monastery was turned back over to the lamas and Erdene Zuu is once more a place of worship. Just outside the monastery wall are two of the four original stone turtles, ancient guardians of Karakorum.