No one knows why the culture declined and the cities were covered by encroaching forest until rediscovery in the 19th century. Possible causes include exhaustion of the cornfields by overpopulation, climatic changes, hurricanes, pestilences of epidemic proportions, wars, and insurrection. Far to the north at the tip of Yucat n the New Empire waxed while the Old Empire waned. Archaeologists trace transition routes through Palenque in Chiapas, via Mirador and Rio Bec in Quintana Roo, and around Cob , where a network of causeway roads called sacbes connect distant cities. The physical environment of the peninsula of Yucat n differs from that of the Pet n. It too is lowland and limestone but arid and covered with desert scrub.
Water is scarce and seasonal, draining underground via sinkholes and subterranean streams.
Where the water table reaches the surface or the limestone layer can be breached, a cenote, or well, provides water for settlement and cultivation. Chaltunes are man-made cisterns lined with plaster to catch rainwater runoff. The themes of art and architecture duplicate Tula, the original capital in the highlands, with emphasis on the images and symbols of the feathered serpent. The Quetzalcoatl portal supported the lintel over the entrance to the Temple of the Warriors, and the memoirs of the associated military orders of Jaguar and Eagle are carved into the Court of the Thousand Columns. Inside, the red Jaguar throne is encrusted with pieces of precious jade.