The Pentagon Barracks of East Baton Rouge Parish has been won and lost by the Spanish, French, and the British, and even has the distinction of being the site of the birth of a nation - the short-lived Republic of West Florida. During it's use as a military post, many famous men and public figures served or visited, including Lafayette, Robert E. Lee, George Custer, Jefferson Davis and Abraham Lincoln. The British erected a dirt fort on the site of the barracks in 1779, which was soon captured by the Spanish Governor of Louisiana, Bernardo de Galvez. Not wanting to be under the rule of Spain, the citizens of the West Florida Territory revolted and in September of 1810 raised the flag over the fort declaring their independence and announcing the birth of the Republic of West Florida. The citizens then turned the area over to the United States on December 10, 1810. The fort served as the assembly point for American troops going to the Creek War in 1813-1814 and to the Battle of New Orleans in 1814-15. A major expansion of the post was made in 1819-1823 when new barracks were built and a large Arsenal Depot was established to serve the southwestern United States. The four, two-story brick buildings were built in 1825 after six years of planning. Captain James Gadsden of the U.S. Army, who prepared the schematics for the barracks, headed the construction. Originally, there were five buildings, Gadsden having intended for a group of buildings arranged in a pentagon-shaped configuration to be erected for the boarding of enlisted soldiers.
The fort remained an U.S. military post until 1861 when it was seized and captured by the State of Louisiana, who turned the operation of the arsenal over to the Confederacy. However, in 1862 during the Battle of Baton Rouge, Federal troops reclaimed the garrison and renamed it Fort Williams for the late commander who died in the battle. After the Civil War, in 1884, the General Assembly of Louisiana passed a resolution allocating the full usage of the buildings and grounds of the Pentagon Barracks to Louisiana State University. The University gained full possession of the grounds in 1886.