Castillo de San Marcos National Monument

The Castillo de San Marcos is a stone fortress built from coquina, a local shell rock, with four diamond-shaped bastions and a moat encircling the entire structure. The layout allows visitors to walk along the top walls and explore interior rooms, barracks, and a central courtyard.

Spanish engineers started construction in 1672 to defend St. Augustine against repeated attacks, finishing the main structure around 1695. The fortress later survived sieges, came under British control, and eventually became a United States military post.

The fortress walls tell stories of contact between Spanish, British, and American powers who each left their mark on the place. Walking through the rooms and courtyards today, you can sense how different cultures shaped this space over centuries.

You reach the fortress by walking across a footbridge over the moat, and you can explore the grounds at your own pace throughout the day. The experience is most enjoyable in the morning or early afternoon when crowds are lighter and the temperature is cooler.

The walls are built from coquina, a material made of crushed shells and sand, which absorbs cannonballs instead of shattering. This unusual building material made conventional artillery fire largely ineffective against the fortress.

Location: Saint Johns County

Operator: National Park Service

Website: https://nps.gov/casa

GPS coordinates: 29.89743,-81.31185

Latest update: December 11, 2025 18:08