El Zócalo is a term used to refer to the main plaza of a Mexican town. It is believed that the word comes from the Italian term zoccolo, which means plinth or pedestal. In the 19th century, a pedestal was set up in the center of Mexico City's main square that was to be the base for a monument that would commemorate Mexican independence. The statue was never put in place and people began to refer to the square itself as Zócalo. Now in many towns in Mexico, the main square is called the Zócalo.
Colonial Town Planning
In 1573, King Philip II ordained in the Laws of the Indies that colonial towns in Mexico and other Spanish colonies should be planned in a certain manner. They were to be laid out in a grid pattern with a rectangular plaza in the center surrounded by straight streets that intersect at right angles. The church was to be located on one side (usually the east) of the plaza, and the government building was to be built on the opposite side. Buildings surrounding the plaza would have arcades to allow merchants to conveniently set up shop there. The central plaza was thus designed to be the religious, political, economic and cultural heart of the city.
Most of Mexico's colonial towns reflect this design, but there are some, such as the mining towns of Taxco and Guanajuato, which were built on locations with uneven topography where this plan could not be fully implemented. These towns have windy streets instead of the straight streets in an even grid pattern that we usually see.
The Mexico City Zócalo
The Mexico City Zocalo is the original, most representative, and most famous one. Its official name is Plaza de la Constitución. It is located over the ruins of the Aztec capital city Tenochtitlan.
The square was built inside the original Sacred Precinct of the Aztecs and was part of its Templo Mayor, the main temple of the Aztecs, dedicated to the gods Huitzilopochtli (the god of war) and Tlaloc (the rain god). It bounded on the east with the so-called "New Houses" of Motecuhzoma Xocoyotzin and on the west by the "Casas Viejas" or Palace of Axayácatl. After the arrival of the Spaniards in the 1500s, the Templo Mayor was razed and the Spanish builders used stones from it and other Aztec buildings to prepare the new Plaza Mayor in the year 1524. The remains of the main temple of the Aztecs can be seen in the Templo Mayor archaeological site located just to the northeast of the plaza, beside the Mexico City Metropolitan Cathedral.
Throughout its history, the plaza has gone through many incarnations. Gardens, monuments, circuses, markets, tram routes, fountains and other ornaments were installed and removed many times. In 1956 the square acquired its current austere appearance: a huge paved surface of 830 by 500 feet (195 x 240 meters) with just a large flag in the center.
Currently, the Zócalo iron is used as a venue for protest demonstrations, recreational activities such as an ice rink during the Christmas season, concerts, exhibitions and book fairs or as a large collection center to summon the support of Mexicans in the event of natural disasters. The annual "Grito" ceremony is held in the Zócalo each year to celebrate Mexico's Independence Day on the 15th of September. This space is also the location of marches and sometimes protests.
If you want to have a good view of the Mexico City Zócalo, there are a few restaurants and cafes that offer panoramic views such as the restaurant of the Gran Hotel Ciudad de México, or that of the Best Western Hotel Majestic. The Balcón del Zócalo also offers good views and is located in the Hotel Zócalo Central.
The zócalos of other cities may have trees and a bandstand in the center like the Oaxaca City Zócalo and Guadalajara's Plaza de Armas, or a fountain, like in Puebla's Zócalo. They often have bars and cafes in the arcades surrounding them, so they're a nice place to take a break from sightseeing and enjoy some people watching.
By Any Other Name...
The term Zócalo is common, but some cities in Mexico use other words to refer to their main square. In San Miguel de Allende, the main square is usually referred to as El Jardín and in Mérida it's called La Plaza Grande. When in doubt you can ask for "la plaza principal" or "plaza mayor" and everyone will know what you are talking about.