The Castillo de San Marcos National Monument, located in St. Augustine, Florida, is the oldest masonry fort in the continental United States. Constructed by the Spanish between 1672 and 1695, the fort was built to protect Spain's interests in the New World and to defend the city of St. Augustine from potential invaders. Its unique star-shaped design and coquina stone walls made it a formidable structure that withstood numerous attacks over the centuries. The fort has served various roles throughout its history, including as a military prison and a symbol of colonial power. Today, visitors can explore its well-preserved bastions, watch historical reenactments, and learn about the diverse cultures that have influenced the region. The Castillo stands as a testament to the rich and complex history of America's oldest city.