Chichen Itza, Mexico, satellite image. North is at top. The ruins of this ancient city, built by the Mayan civilisation, are at centre, surrounded by forest, roads and an airstrip (upper centre). The main monuments and buildings date from the 11th and 12th centuries. The large pyramid (centre) is the Temple of Kukulkan. The pyramid's alignment means that sunlight shines down the northern stairway at sunset on the equinoxes. The sunlight and shadow sliding down the stairs is thought to represent Kukulkan, the Feathered Serpent god. The site also aligns with the solstices, and the number of steps (365, representing days of the year) and terraces may represent periods of the Mayan calendar. Image obtained by the Ikonos satellite on 5 March 2001.