Before the Spaniards demolished it, the Teocalli of Tenochtitlán covered the site where the cathedral now stands, as well as the blocks to its north and east. It wasn’t until 1978, after electricity workers happened on an eight-tonne stone-disc carving of the Aztec goddess Coyolxauhqui, that the decision was taken to demolish colonial buildings and excavate the Templo Mayor.

The temple is thought to be on the exact spot where the Aztecs saw their symbolic eagle perching on a cactus with a snake in its beak – the symbol of Mexico today. In Aztec belief this was, literally, the center of the universe.

Like other sacred buildings in Tenochtitlán, the temple was enlarged several times, with each rebuilding accompanied by the sacrifice of captured warriors. What we see today are sections of the temple’s seven different phases. At the center is a platform dating from about 1400. On its southern half, a sacrificial stone stands in front of a shrine to Huizilopochtli, the Aztec war god. On the northern half is a chac-mool (a Maya reclining figure) before a shrine to the water god, Tláloc. By the time the Spanish arrived, a 40m-high double pyramid towered above this spot, with steep twin stairways climbing to shrines of the two gods.

The entrance to the temple site and museum is east of the cathedral, across the hectic Plaza del Templo Mayor. Authorized tour guides (with Sectur ID) offer their services by the entrance. Alternatively, rent an audio guide – available in English.

The on-site Museo del Templo Mayor (included in the site’s admission price) houses a model of Tenochtitlán and artifacts from the site, and gives a good overview of Aztec, aka Mexica, civilization. Pride of place is given to the great wheel-like stone of Coyolxauhqui (She of Bells on her Cheek), best viewed from the top-floor vantage point. She is shown decapitated, the result of her murder by Huizilopochtli, her brother, who also killed his 400 brothers en route to becoming top god.

Ongoing excavation continues to turn up major pieces. Just west of the temple, a monolithic stone carved with the image of Tlaltecuhtli, the goddess of earth fertility, was unearthed in October 2006 and is now prominently displayed on the museum's 1st floor.

Another key find was made in 2011 when a ceremonial platform dating from 1469 was uncovered. Based on historical documents, archaeologists believe the 15m structure was used to cremate Aztec rulers. A recent dig also turned up what archaeologists believe is the trunk of a sacred tree found at a newly discovered burial site at the foot of the temple. Now more than ever, researchers feel they are inching closer to the first discovery of an Aztec emperor’s tomb.