The main marketplace was in Tlatelolco, Tenochtitlan’s sister city.  Cortés the conqueror estimated it was twice the size of the city of Seville with about 60,000 people trading daily.
Bernal Diaz del Castillo, who was a foot soldier in the army of Hernán Cortés that conquered the Aztec empire in 1519-1522, described the moment when the Spaniards first saw the great city of Tenochtitlan.

Tenochtitlan Market in Tlaltelolco

Tlatelolco Market

And when we saw all those cities and villages built in the water, and other great towns on dry land, and that straight and level causeway leading to Mexico [i.e. Tenochtitlán], we were astounded. These great towns and cues [i.e., temples] and buildings rising from the water, all made of stone, seemed like an enchanted vision from the tale of Amadis. Indeed, some of our soldiers asked whether it was not all a dream.”

Mexican National  Emblem

It is so that the eagle perched on a prickly pear tree-nopal– devouring a snake came to be one of Mexico’s most important symbols. It is the fundamental element of the coat of arms or national shield as well as an essential part of the Mexican Flag.