The entire historic site of San Juan with its different monumental components maintains, at the present, a balance between constructed and non-constructed zones. The Fortaleza is tangibly associated with the history of the New World and its explorers and colonists.
For the explorers and the colonists of the New World who came from the east, Puerto Rico was an obligatory stopping-place in the Caribbean. From this evolved its primordial strategic role at the beginning of the Spanish colonization. The island was for centuries a stake disputed by the Spanish, French, English and Dutch. The fortifications of the bay of San Juan, the magnificent port to which Puerto Rico owes its name, bear witness to its long military history.
San Juan had the first municipal government in the New World outside Santo Domingo, as well as the first military presidios in Spanish America. By the 19th century, the old city had become a charming residential and commercial district. The city itself, with its institutional buildings, museums, houses, churches, plazas and commercial buildings, is part of the San Juan Historic Zone which is administered by municipal, State and Federal agencies.
La Fortaleza is one among several, of the fortresses which protect it. Over the centuries, San Juan in fact protected Spain's empire against Carib Indians, pirates and the warships of other countries. This vast, coherent defensive system with ramparts, fortlets and fortresses, attesting formerly to its effectiveness and today to its historic significance. The principal components of this defensive system are, starting in the south:
- La Fortaleza, founded in 1530-40, enlarged at various periods, and heavily modified after 1846, is an exemplary monument of Hispano-American colonial architecture. It served at once as an arsenal, prison, and residence for the Governor-General of the island;
- El Morro, built to protect San Juan Bay, is situated on a rocky peak of land on the western extremity of the island. The fort is a triangular bastion perfectly conceived according to the strategy of the second half of the 18th century, when it was entirely remodelled. It eventually developed into a masterpiece of military engineering with stout walls, carefully planned steps and ramps for moving men and artillery. By the end of the 18th century, more than 400 cannon defended the fort, making it almost impregnable.
- San Cristóbal, with its dependencies, is another accomplished example of the military architecture of the second half of the 18th century.
- San Juan National Historic Site includes forts, bastions, powder houses, wall and El Cañuelo Fort, also called San Juan de la Cruz - defensive fortifications that once surrounded the old colonial portion of San Juan, Puerto Rico. El Cañuelo Fort is located at the Isla de Cabras at the western end of the entrance to San Juan Bay.