Xochicalco

Xochicalco, "in the house of flowers" in Nahuatl, is one of the great archaeological sites of central Mexico and a UNESCO World Heritage Site since 1999. It rose on a cluster of hills west of Xochitepec after the fall of Teotihuacan and reached its peak between about 650 and 900 AD, when it may have held up to 20,000 people. Its builders reshaped the hills into terraces and ringed them with moats, walls and ramps, creating a fortified city that controlled trade routes toward Guerrero, Oaxaca, the Gulf coast and the Maya area.

The highlight is the Temple of the Feathered Serpent, whose sloping walls are covered with relief carvings of plumed serpents, seated figures in a Maya-like style and glyphs that seem to name tributary towns. Around it are palaces, step pyramids, three ballcourts, steam baths and a line of round altars. Best known after the temple is the observatory, a cave with a carved shaft in its roof: between late April and mid-August sunlight shines down into it, and on the two zenith passages, around May 14–15 and July 28–29, the sun's image falls straight onto the floor at midday.

Around 900 AD the city was burned and abandoned quickly. Today the site has a well-designed museum at the entrance, with stelae and objects found during excavations.