San Juan is the capital city and most populous municipality in Puerto Rico, an unincorporated territory, and insular area of the United States. San Juan was founded by Spanish colonists in 1521, who called it Ciudad de Puerto Rico (Spanish for "Rich Port City").
Puerto Rico's capital is the second oldest European-established capital city in the Americas, after Santo Domingo, in the Dominican Republic, founded in 1496, and is the oldest European-established city under United States sovereignty. Several historical buildings are located in the historic district of Old San Juan; among the most notable are the city's former defensive walls, Fort San Felipe del Morro and Fort San Cristóbal, and La Fortaleza, the oldest executive mansion in continuous use in the Americas.