Its location is on one of the great ancient trails leading from the north into the Valley of Mexico.[93] The ruins of the old town are upon an elevation about 100 feet in height, whose summit presents a level surface in the shape of an irregular triangle some 800 yards long, with a central width of 300 yards, the apex to the south-east, where the face of the hill is fortified by a rough stone wall.[94] It is a natural hill, overlooking a small muddy creek, called the _Rio de Tula_.[95] Yet this unpretending mound is the celebrated _Coatepetl_, Serpent-Mount, or Snake-Hill, famous in Nahuatl legend, and the central figure in all the wonderful stories about the Toltecs.[96] The remains of the artificial tumuli and walls, which are abundantly scattered over the summit, show that, like the pueblos of New Mexico, they were built of large sun-baked bricks mingled with stones, rough or trimmed, and both walls and floors were laid in a firm cement, which was usually painted of different colors. Hence probably the name _Palpan_, “amid the colors,” which tradition says was applied to these structures on the Coatepetl.[97] The stone-work, represented by a few broken fragments, appears equal, but not superior, to that of the Valley of Mexico. Both the free and the attached column occur, and figure-carving was known, as a few weather-beaten relics testify. The houses contained many rooms, on different levels, and the roofs were flat. They were no doubt mostly communal structures. At the foot of the Serpent-Hill is a level plain, but little above the river, on which is the modern village with its corn-fields. These geographical particulars are necessary to understand the ancient legend, and with them in mind its real purport is evident.[98]