La Fortaleza, (The Fortress) is the current official residence of the Governor of Puerto Rico. It was built between 1533 and 1540 to defend the harbor of San Juan. The structure is also known as Palacio de Santa Catalina (Santa Catalina Palace). It is the oldest executive mansion in the New World. It was listed by UNESCO in 1983 as a World Heritage Site.
During the 1640 reconstruction, the chapel of Santa Catalina, which originally existed outside of the walls, was demolished and was integrated to the walls of the structure. This would give rise to the name of Santa Catalina's Palace.
La Fortaleza was the first defensive fortification built for the city of San Juan, and the first of a series of military structures built to protect the city. The construction was authorized by Charles V as a defense against attacks from the European powers of the day and Carib Indians.
Initially, the structure consisted of four walls enclosing an interior patio with a circular tower known as the Homage Tower. From the top of the tower, the governor, following military tradition, would take oaths of fidelity at critical moments to the Queen and the King of Spain. Later, a second tower named the Austral Tower was constructed.
At present, the complex consists of a few attached buildings with formal living quarters in the second floor, and private quarters in the third. It overlooks the high city walls that front the bay, and within the north perimeter of the house are sheltered gardens and a swimming pool.
Since the 16th century, La Fortaleza has acted as the residence of the Governor of Puerto Rico, making it the oldest executive mansion in continuous use in the Americas. On November 27, 1822 the tradition of executive mansion was officialized. The fortress underwent a massive reconstruction in 1846 to change its military appearance into a palatial facade.