Castillo de San Marcos by the Numbers: Begun Oct. 2, 1672, a Coquina Fort With 4 Bastions That Survived 2 Sieges

ST. AUGUSTINE, Fla. - The first coquina stones of the Castillo de San Marcos were laid on Oct. 2, 1672, and the core of the fort was finished in 1695, according to Wikipedia. It is the oldest masonry fort in the continental United States, standing on the western shore of Matanzas Bay. The National Park Service runs it as Castillo de San Marcos National Monument.

The fort has flown Spanish, British and American flags over its long history, and its walls of shell stone are still the first thing most visitors notice. The Spanish handed it to the British in 1763 and the Americans took it over after 1821. Here are the key numbers and dates, from the first stones to the entry fee today.

The Castillo by the numbers

Built from shell

The fort was designed by Spanish engineer Ignacio Daza, according to Wikipedia. It is built of coquina, a sedimentary rock made of bonded ancient shells, which is why its walls look pocked and golden rather than smooth. A close-up photograph of the wall shows the shell fragments embedded in the stone.

The reason the stone mattered is practical. Coquina is soft enough to absorb impact, so cannon shot tends to lodge in it rather than shatter it. That is the commonly cited explanation for the fort's endurance, though the sources reviewed for this story do not quantify it.

The fort has four corner bastions and a ravelin, a triangular outwork that protects the sally port, according to Wikipedia. A drawbridge beside the ravelin serves as the entrance today, according to a Commons photo description. A moat runs around the walls.

Two sieges

The first came in 1702, when Carolina Gov. James Moore Sr. besieged the fort starting in November, and it lasted about two months, according to Wikipedia. The fort held. The second came in 1740, when Georgia founder James Oglethorpe's forces bombarded it for 27 days before retreating.

The exterior wall was raised from 26 to 33 feet in the 1738 rebuild under Pedro Ruiz de Olano, according to Wikipedia. That rebuild came two years before the 1740 siege. The 1740 siege tested that rebuilt wall.

Flags and a new name

Spain turned the Castillo over to Britain on July 21, 1763, and the fort was renamed Fort St. Mark. Spanish troops returned to St. Augustine on July 12, 1784. After the United States took possession in 1821, the fort was renamed Fort Marion, honoring Revolutionary War hero Francis Marion, according to Wikipedia.

Beginning in 1875, Native American prisoners from the western Indian Wars were held at the fort under Richard Henry Pratt, who improved their conditions, according to Wikipedia. About 491 Apaches were held there in 1886 and 1887, including members of Geronimo's band, though Geronimo himself was sent to Fort Pickens, according to the same account. By then the fort carried the name Fort Marion, which it received after 1821.

Planning a visit

The park's address is 1 South Castillo Drive, St. Augustine, FL 32084, and its phone number is 904-829-6506, according to the National Park Service. The NPS fee page, last updated in March 2024, lists a $15 standard pass for adults ages 16 and older, valid for seven consecutive days, and says children 15 and under are free with an adult. An annual pass is listed at $45.

The park is cashless and accepts only credit and debit cards, according to the same page. The city lot in front of the fort charges $2.50 an hour, and a city garage is about a block away. Because the fee page is not recent, visitors should confirm prices and hours with the park before they go, since this story could not verify current operating hours.