Located in the heart of the historic centre of Mexico City, Plaza de la Constitution, informally known as the Zócalo or the main square of the city, is one of the largest squares in the world, flanked by a huge flag pole bearing the Mexican flag. However, occupying an almost rectangular area of approximately 503751 sq feet (46,800 sq m), it was the main ceremonial centre in the Aztec city of Tenochtitlan and throughout its history it has been known by several names like Plaza de Armas, Plaza Principal, Plaza Mayor and Plaza del Palacio. Finally, it earned its current name in 1813, in honour of the Constitution of Cádiz, better known as the Spanish Constitution, promulgated in the previous year (1812) in Cádiz.

Since Aztec times, it served as the gathering place for the Mexicans, the site to celebrate ceremonies, military parades, royal proclamations, Independence ceremonies and modern religious events. It also has been the site of important events in the various stages of the history of Mexico and during five centuries of history, it has undergone changes in the elements and buildings that surround it and its current appearance dates back to 1958.

The Plaza de la Constitucion, which overlooks Matanzas Bay and the approach to the Bridge of Lions, is located just one block southwest of the Templo Mayor, the great temple, destroyed by the Spanish in 1521, which according to Aztec legend and mythology was the centre of the universe. The plaza, which once was a slave market, also served as a public marketplace where ships docked at the nearby wharves used to sell their cargoes.

Later, it variously served as a forum for mass protests. This was the place where Union naval officers reclaimed the city from the Confederacy in 1862. During the civil rights movement, the plaza was the site of numerous peaceful protests. It is bordered by the National Palace to the east, the Old Portal de Mercaderes to the west, the Mexico City Metropolitan Cathedral to the north, the Federal District Buildings to the south and the building of the Nacional Monte de Piedad at the north-west corner.

The Metropolitan Cathedral, officially known as the Metropolitan Cathedral of the Assumption of the Most Blessed Virgin Mary into Heaven and built on the site of the Templo Mayor, is the spiritual centre of the Aztec capital.

Located to the north of the Plaza de la Constitucion, it is one of the most treasured architectural masterpieces in Mexico, as well as one of the largest and oldest cathedrals in Latin America. As it took three centuries to build, from 1573 to 1813, its architecture reflects an amalgamation of the three distinct styles that dominated during its construction, baroque, neo-classical and neo-renaissance. It consists of two bell towers, a central dome and three main portals, along with four facades containing portals, flanked with columns and statues. While the main facade of the church has a relief showing the Assumption of the Virgin Mary, to whom this cathedral is dedicated, the interior consisting of five naves with 14 chapels and five altarpieces, known as the Altar of Forgiveness, the Altar of the Kings, the main altar, the Altar of Resurrected Jesus and the Altar of the Virgin of Zapopan. The octagonal drum of the cathedral, raised to the centre of the cruise and placed on four columns is topped by a lantern.

The south of the Plaza de la Constitucion is occupied by the Old City Hall Palace and the Government buildings. The Old City Hall Palace, a World Heritage Site since 1987, is a museum that houses historical heritage such as the Cabildos Hall and the Francisco Gamoneda Documentation Centre and office of the Government of Mexico City. The Mexico City administrative buildings that house offices of the governing authority of Mexico City are two buildings on the south side of the Plaza de la Constitucion, divided by the avenue Avenida 20 de Noviembre. The building to the west of 20 de Noviembre is the older one and the one to the east is newer, built in the 20th century.

Located to the east of the Plaza de la Constitucion, the National Palace, which served as a palace for the ruling class of Mexico since the Aztec Empire, is now classified as a government building and houses some of the offices of both the Federal Treasury and the National Archives. The more than 600 feet (200 m) long palace with its red tezontle facade fills the entire east side of the square, while its facade is bordered on the north and south by two towers and includes three main doorways, leading to different parts of the building. The highlights of the massive building are several murals, created by Diego Rivera, painted in a panoramic style across the walls of the palace, depicting the stages of Mexican history, from pre-Columbian days to the current age. The ornate palace contains several gardens, murals and fountains in the Spanish Renaissance architectural style.

Several commercial buildings, such as the Portal de Mercaderes, administrative buildings and hotels are located to the west of the Plaza de la Constitucion. Today the west side of the block is dominated by two buildings, with Madero Street dividing them as it runs from the Palacio de Bellas Artes towards the Zócalo. The buildings on the south side of Madero Street are occupied by offices on the upper floors and shops at ground level. The southern part of the building is filled with jewellery stores on the ground floor.

The Plaza de la Constitucion, which serves as the focal point of the city’s historic district, hosts a variety of outdoor events like different social, cultural and religious festivals throughout the year. Apart from that, it also serves as the backdrop for the Easter Parade, which features locals dressed in their finest spring attire. Every day the Mexican soldiers march into the square at sunset to remove the flag, providing an excellent photo opportunity. The locals and the visitors also enjoy the free Thursday night concerts from Memorial Day to Labour Day, when two million tiny white lights trace the outline of the historic buildings and the branches of historic oak trees surrounding the plaza.