Chichen Itza was a large Mayan city on the Yucatan Peninsula of Mexico. The city was established in the early 400's AD and was inhabited until 900 AD. At its height, it is believed that as many as 50,000 people lived in the city. After the Spanish conquest of the Yucatan in 1547, many of the abandoned city's structures received Spanish names. The city was later forgotten and covered by jungle. The city was rediscovered in the 1840's. This is El Castillo (the Castle) or Pyramid of Kukulkan. The large square pyramid has a small temple at the top.