The Zócalo is the common name of the main square in central Mexico City. Prior to the colonial period, it was the main ceremonial center in the Aztec city of Tenochtitlan. 

The plaza used to be known simply as the "Main Square" or "Arms Square", and today its formal name is Plaza de la Constitución.

It has been a gathering place for Mexicans since Aztec times, having been the site of Mexican ceremonies, the swearing-in of viceroys, royal proclamations, military parades, Independence ceremonies, and modern religious events such as the festivals of Holy Week and Corpus Christi. It has received foreign heads of state and is the main venue for both national celebrations and national protests.

- Wikipedia