For the best views of the Castillo’s overall layout and its surroundings, climb up the stars to the upper gun deck. The fort has a distinct star-shape architectural design consisting of four diamond-shape bastions named San Augustin, San Carlos, San Pablo, and San Pedro. The bastions typically feature thick walls packed solidly with rubble and sand to offer extra support for withstanding the weight of the cannons.
The bastions are connected by four walls known as “curtains,” and together, they form the artillery fortification. This design served defensive and offensive purposes in the age of gunpowder warfare. While capable of withstanding the impact from cannon projectiles, the fortification is also effective for mounting and firing cannons at potential intruders. As of 1740, the fort had more than 70 cannons of varying sizes, and the largest of them could fire up to three and a half miles.
One reason that the fort has managed to survive through numerous blasts and attacks is due to the use of coquina, a semi-rare sedimentary limestone found in northeast Florida. The Castillo was built with more than 400,000 blocks of coquina, and its outer walls were as thick as 1 -feet. As a building material, coquina is light and porous which helps the fortress cushion the impact from cannon projectiles rather than shatter under pressure. Even up until today, round dents could still be seen in the external walls, which are evidences of the coquina’s shock-absorbing abilities.
For many visitors, one of the highlights of their visit is the historic weapons demonstration that takes place every Friday, Saturday, and Sunday at the gun deck. Rangers and volunteers dressed in period costumes will re-enact scenes from the colonial era, including the firing of cannons, which is a dramatic and entertaining sight to behold. Although the cannons used for demonstrations are reproductions, many originals are exhibited throughout the facility. Look out for the positioning of the cannons in the bastions. They are placed strategically, just as they would have been during the Spanish period, to illustrate how the layout was designed to ambush the enemy in artillery crossfire.
Entrance and Courtyard
There is only one entrance and exit to the fortress. All visitors will need to walk through the ravelin, which is a triangular construction located on the outer section of the fortress. The fortification was intended to protect the entrance to the fort, though it was never completed as planned. Two working drawbridge reconstructions link the outside world to the ravelin and the ravelin to the inner parts of the fortress.
The entrance leads to the ground floor of the fortress. Centrally located is the Plaza de Armas, or central courtyard, that served two main functions under the Spaniards. On a daily basis, it was used for conducting military drills and cannon procedures, and during wartime, it was designed to be a place of refuge for the town’s people. This was the case in 1702 when the town came under siege by the English. Almost 1,500 soldiers and civilians took refuge inside the fortress for 51 days.
Many of the rooms surrounding the courtyard were used as warehouses to store food and military supplies such as gunpowder, ammunition, and tools. Given that St. Augustine was not self-sufficient, these stockpiles were critical defense mechanisms during periods of siege. Visitors can enter some of these casemates to understand how the function of these rooms changed during the different chapters of its history.