Kukulcán, the Feathered Serpent, is the Yucatec counterpart of the central Mexican Quetzalcoatl, a deity of the sky and wind bound up with rulership and the founding of cities. Diego de Landa relates that Kukulcán arrived from the west, ruled justly at Chichén Itzá, was instrumental in the founding of Mayapán, and after ordering the affairs of the land returned westward and was thereafter worshipped as a god; his feast was celebrated on the day 16 Xul. He is remembered in the Books of Chilam Balam under Mexicanized titles such as Nacxit Xuchit. His most famous monument is the great pyramid at Chichén Itzá, El Castillo, on whose balustrade the equinox sun casts the undulating shadow of the descending serpent.