This is the oldest masonry fort from the colonel area, and still stands tall and strong. After nearly twenty three years, the fort finished completion in 1695. The uniquely shaped fort was not an easy target. It was originally built by the Spanish to claim that part of Florida, to scare off the British from settling claim to the area, and to fight against pirates. The fort is built out of a shell filled rock, with lots of air pockets, called Coquina. It was used because it was the only stone available but it provided an unknown advantage. Because the stone has pockets of air and is fairly soft when cannon balls hit the wall instead of shattering the stone, it just absorbed the cannon ball. The walls were build fourteen feet thick and thirty feet tall. The fortress also had a moat that proved very valuable. The eight feet deep moat was left dry most of the time, but could be flooded if needed. They left it dry and grassy because it housed all of their cattle. During times of siege they could hold their own for months because of the food supply. Around the moat they built tall slopes, making it difficult for the enemy to attack or even see their opponents. Another smart trick the fort used was the the hot shot oven. They would place cannon balls in an oven to get them red hot, then they would shoot those flaming fireballs at ships and cause the ship to catch fire. The fort had an array of cannons and canon balls, from a six lbs ball to a thirty two lbs mortar shell. At the fort they now do live cannon reenactments on the weekend, watch as they fire a cannon and use the same steps used hundreds of years ago. Come visit this historic sight like no other at, The Castillo de San Marcos Fort.