San Juan is the capital and most populous municipality of Puerto Rico, situated on the island's northeastern coast along the Atlantic Ocean. It is one of the oldest European-founded cities in the Americas: Spanish colonists established the settlement in 1521, moving it to a rocky islet at the entrance to a sheltered harbor after Juan Ponce de León had founded an earlier settlement at Caparra in 1508. Today San Juan is the oldest city under United States jurisdiction and the center of a metropolitan area of more than two million people. The city is anchored by Old San Juan, a walled colonial district of cobblestone streets and colorful Spanish buildings, guarded by the historic fortresses of Castillo San Felipe del Morro and Castillo San Cristóbal. Beyond the old quarter, San Juan stretches east along the coast through the upscale beachfront of Condado, the arts district of Santurce, the residential enclave of Ocean Park, and the resort area of Isla Verde, with the financial district of Hato Rey and the university district of Río Piedras inland. San Juan functions as the island's economic, cultural, and transportation hub. Its economy centers on tourism, finance, government, and trade, with the Port of San Juan serving as a major Caribbean cruise and cargo gateway and Luis Muñoz Marín International Airport handling millions of passengers a year. The Tren Urbano, the Caribbean's first rapid transit system, links San Juan with neighboring Bayamón and Guaynabo. The city is also home to the main campus of the University of Puerto Rico and a concentration of the island's institutions. For homebuyers, San Juan offers an unusually broad spectrum, from historic Old San Juan residences to beachfront condominiums and inland single-family homes. It appeals to professionals, government and finance workers, students and academics, and those drawn to a tropical, urban, culturally rich capital with direct air and sea connections to the mainland United States and beyond.