Many towns in South America have a Plaza de Armas. Most cities constructed by the Spanish Conquistadores were designed on a standard military fashion based on a grid pattern, taken from the Roman Castrum, of which one of the blocks would be left vacant to form the Plaza de Armas. It is often surrounded by governmental buildings, churches, and other structures of cultural or political significance.
Santiago is no exception. It has a grand Plaza de Armas surrounded by a cathedral and various government buildings.
View a video of the Plaza de Armas on Google Maps