Castillo De San Marcos Interior Wall, St. Augustine Editorial Image

The Castillo de San Marcos is the oldest masonry fort in the continental United States, in St. Augustine Florida. The fort was started in 1672, even though it later fell into English hands. St. Augustine became capital the British East Florida, and Castillo de San Marcos became Fort St. Mark. In 1783, Florida went back into Spanish hands until 1819 when Spain signed the Adams�On�s Treaty which ceded Florida to the United States in 1821, and the Fort was named Fort Marion after a famous American Revolutionary War hero Francis Marion. In 1942 the original name Castillo de San Marcos was restored by an Act of Congress. The fort became a National Monument in 1924, and after 251 years of continuous military possession, was deactivated in 1933. The 20.48-acre (8.29 ha) site was then turned over to the United States National Park Service.