According to Aztec sources, Templo Mayor was built on this spot because an eagle was seen perched on a cactus devouring a snake, in fulfillment of a prophecy.
Construction on the temple began sometime after 1325 AD and was enlarged over the next two centuries. At the time of the 1521 Spanish Conquest, the site was the center of religious life for the city of 300,000.
The temple was almost completely destroyed by the Spaniards after their conquest of Tenochtitlan and was completely lost until an Aztec carving was discovered in the heart of Mexico City in 1978. This prompted extensive excavations, which uncovered the ruins of Templo Mayor.
Templo Mayor is a large stone pyramid with the familiar wide staircases and temples seen throughout Mexico. Twin temples on the summit of Templo Mayor were dedicated to Huitzilopochtli, the god of war, and Tlaloc, the rain god.
These gods were frequently appeased by human sacrifices, which took place on an altar high on the pyramid. The victim was placed face up on a block of volcanic stone and killed with an obsidian knife. The body was then thrown down the staircase.
A carved round stone once lay on the lower platform of the pyramid (it's now in the site museum), depicting the severed limbs of the Aztec moon goddess Coyolxauhqui. According to Aztec mythology, she was slain by her brother Huitzilopochtli because she had killed their mother. The goddess ruled the night, but died at every sunrise, slain by the sun god.
Two snake heads guard the foot of the main staircase and appear elsewhere in the temple. Templo Mayor was a symbolic re-creation of Coatepec, "the Hill of the Serpent," a mythical sacred place. The Aztecs referred to Templo Mayor as Coatepec.
Some of the site can be seen in situ, but most of the Templo Mayor artifacts are displayed in the adjacent site museum. The museum superbly illustrates the variety and splendor of the Aztec Empire, and all 6,000 pieces came from the relatively small plot of excavated ruins just in front of the museum.
Notable pieces found in the temple include the Tzompantli-Shrine or Wall of Skulls, a panel made of rows of human skulls covered with stucco; two identical life-size clay statues of Aztec warriors dressed in eagle costumes; and a stone eagle symbolizing the god Huitzilopochtli, into which the hearts of sacrificial victims were placed. A cutaway model of the Templo Mayor shows the layers and methods of construction.