Archaeologists working at the Teotihuacan archaeological complex north of this capital have found ditches and passageways beneath the plaza in front of the Moon Pyramid, Mexico's National Anthropology and History Institute said.
"Seen from above (these ruins) could look like a lunar landscape filled with craters," the institute said in a statement.
Teams discovered stellae made of green stone, passageways pointing to the symbolic center of the universe and a series of holes filled with river pebbles.
The newly found ruins are all elements of a code that the ancient Teotihuacans elaborated some 1,900 years ago, the statement said.
Teotihuacan was founded in the 2nd century B.C., though the major monuments date mainly circa A.D. 200. The city suffered a sudden collapse in the 7th century.
So far, excavations have focused on the building next to the Moon Pyramid, known as Structure A, a 625-sq. meter (6,720-sq. foot) walled courtyard containing 10 small altars.