The Pyramids of the Sun and the Moon, echoing the shape of the mountains surrounding the valley, served as focal points for Teotihuacan's urban layout. Beneath the pyramids are earlier structures; perhaps even tombs of Teotihuacan rulers are to be found within their stone walls. When the Pyramid of the Sun was completed circa 200 A.D., it was some 63 meters tall and 215 meters square. One of the largest structures ever built in the ancient Americas, its aspect today is the result of reconstruction and consolidation carried out in the early part of the twentieth century. Excavations in 1971 directly under the Pyramid of the Sun revealed a tunnel-like cave, ending in a cloverleaf-shaped set of chambers, apparently the scene of numerous ancient fire and water rituals. This cave may have been a "place of emergence"the "womb" from which the first humans came into the world in central Mexican thought. Caves are a key part of symbolic imagery associated with creation myths and the underworld throughout Mesoamerican history. The location and orientation of this cave may have been the impetus for the Pyramid of the Sun's alignment and construction.
The Pyramid of the Moon, at the northern end of the Street of the Dead, was probably completed around 250 A.D. Recent excavations near the base of the pyramid staircase have uncovered the tomb of a male skeleton with numerous grave goods of obsidian and greenstone, as well as sacrificial animals. One of the most significant tombs yet discovered at Teotihuacan, it might indicate that even more important tombs lie buried at the heart of the pyramid.