By the 13th century CE, Anahuac - the Valley of Mexico – was occupied by various civilized groups of Toltec descent and Chichimec migrants, who had established a number of different competing city states. Among the last group of people to arrive in the Valley was the barbaric and nomadic tribe of the Mexica, “the people whose face nobody knows”. Official Aztec history claimed they had migrated from their northern homeland, Aztlan, lead by their tribal deity, the war god Huitzilopochtli. According to legend the wandering Mexica had been told by Huitzilopochtli to build their city in the spot where an eagle, perched on a nopal cactus, would be seen eating a snake. They saw the sign they were looking for on a small marshy island in the brackish Lake Texcoco, and in year 2-House (1325 or 1345) established the city of Tenochtitlán there.

Prophecy aside, the more likely reason for settling in such an unprepossessing location was that the Mexica were relatively weak compared to the other groups who had already claimed the land surrounding the lake, and who regarded the barbaric newcomers with suspicion and disdain. However, despite the drawbacks, Tenochtitlán quickly thrived. The swamps between the small islands were drained and the city expanded out from its original small island using chinampas for agriculture and to dry and expand the usable area of land. By the time Hernán Cortés arrived in Tenochtitlán in 1519, the city was home to an estimated 200,000 people, making it one of the largest cities in the world.

"And when we saw so many cities and villages built in the water and other great towns on dry land and that straight and level Causeway going towards Mexico, we were amazed and said that it was like the enchantments they tell of in the legend of Amadis, on account of the great towers and temples and buildings rising from the water, and all built of masonry. And some of our soldiers said that all these things seemed to be a dream...There is so much to ponder in this, and I do not know how to tell it, for never was there seen, nor heard, nor even dreamt, anything like that which we then observed." --Bernal Diaz de Castillo, upon entering Tenochtitlán on 8 November 1511.

As the Aztec empire came to dominate other tribes all around Mexico, the small natural island Tenochtitlán had been founded on was perpetually enlarged. The city grew to become the largest and most powerful in Mesoamerica, covering an estimated 5 sq miles (14 sq. km.), and connected to the mainland by three main causeways leading north, west, and south of the city. These causeways were interrupted by openings that allowed canoes and other traffic to pass freely and removable bridges that also served a defensive purpose.

The city was laid out in a grid pattern divided by canals with rectangular plots of land and houses between. It was divided into four main zones or campan, each of which was divided into 20 districts (calpullis). Each calpulli had its own specialty industry and its own tiyanquiztli (marketplace), but there was also a main marketplace in Tlatelolco. Two double aqueducts, each more than four kilometres long and made of terracotta, provided the city with fresh water from the springs at Chapultepec.

The centre of Tenochtitlán where the main highways met was the focal point of the city and the administrative heart of the empire. The Sacred Precinct, a paved and walled area, was dominated by the double Great Temple of Huizilopochtli and Tlaloc and surrounded by magnificent royal palaces and other public buildings such the temples of Quetzalcoatl and Tezcatlipoca, a very large ball court, and the tzompantli (a rack of human skulls skewered for public exhibition).

Tenochtitlán was eventually conquered by Cortés’s Spanish conquistadores in 1521 after a long siege during which much of the city was destroyed. The rest of the city was largely buried when Mexico City was built upon its ruins, although remnants continue to be uncovered during construction work.

The Great Pyramid or Templo Mayor was the main temple of Tenochtitlan and was dedicated to Huitzilopochtli, the god of war and sun, and Tlaloc the god of rain and fertility. According to the Aztec foundation myth, when the Mexica arrived at Lake Texcoco, they built the first temple to Huitzilopochtli at the place they had seen the eagle perched on a nopal cactus devouring a snake—the sign that this was the place they should settle. This first temple was a simple structure made of mud and wood, but construction of the Templo Mayor began in the year designated 2-Rabbit (1390). It was subsequently re-built seven times and enlarged eleven times - the last time in 1487, when between 3,000 and 84,000 people were sacrificed over 4 days during its reconsecration.

As befitted its importance, the Templo Mayor was always the tallest structure in Tenochtitlán. In the last stage, dating to the time of the arrival of the Spaniards, the pyramidal platform was composed of four sloped tiers with a passage between each level, built on a great platform that measured approximately 80 x 100 meters. It had two stairways of access to the top, where there were two shrines or chapels dedicated to Tlaloc on the left side (as you face the structure), and to Huitzilopochtli on the right side. Each stairway was topped by what are called balustrades, referring to the cube-shaped terminations flanking the stairs while serpent heads were found at the base. The two temples, located at approximately 30 meters in height, had a specific decoration and the entire building was originally covered with stucco and polychrome paint. Numerous smaller buildings and platforms associated with the temple formed a closely-situated complex around its base. A stucco relief depicting a tzompantli, or "skull rack" decorated one platform leading to the temple.

The Templo Mayor was mostly destroyed in 1521 after Tenochtitlán was conquered by Hernán Cortés, and modern Mexico City was built over its ruins. It was rediscovered accidentally on February 21, 1978, when workers laying cables uncovered a huge stone sculpture of Coyolxauhqui. The discovery of this remnant resulted in the archaeological excavations of the Templo Mayor Project, which continues today.