Uxmal, an ancient Maya city of the classical period covering 7500 km2 in el valle de Santa Elena (Santa Ana Valley) in the Puuc region of the southwestern Yucatán Peninsula, is considered one of the most important archaeological sites of Pre-Hispanic Mesoamerica. The site has been designated a UNESCO World Heritage Site in recognition of its significance. No-one knows when the Mayan first settled in Uxmal. The Books of Chilam Balam date its founding to around 569 AD by Hun Uitzil Chac Tutil Xiu, but ceramic evidence points to occupation as early as 800 BC. The ruins on the site were constructed starting in the 6th century AD, with continued expansion over the next few centuries as the city became the cultural, economic and political center of the region, with peak population reaching around 25,000. Its buildings are typical of the Puuc style--with smooth low walls and ornate carvings and friezes embedded within the architecture. Unlike most other pre hispanic towns, Uxmal is laid out in relation to astronomical phenomena, and adapted to the topography of the site. Constructed at the thriving city stopped at some point in the 10th century before the Spanish came, but the dates of and reason for its abandonment are unknown.