The Castillo de San Marcos is the oldest masonry fort in the continental United States. Located on the western shore of Matanzas Bay in the city of St. Augustine, Florida, the fort was designed by the Spanish engineer Ignacio Daza. Construction began in 1672, 107 years after the city's founding by Spanish Admiral and conquistador Pedro Menéndez de Avilés, when Florida was part of the Spanish Empire.