The historic complex of buildings that makes up the old Navy Arsenal is located in the La Puntilla section of Old San Juan, on land that was once a mangrove swamp. The structure was built in 1800 to store weapons and munitions, as well as serving as a workshop for building and repairing Spanish Navy ships. The main façade faces north, and its entrance arch is marked by two pairs of Tuscan-style columns that support a frieze that shows the signs of the zodiac. Above the cornice are three pedestals topped by a royal coat of arms.
After the change in sovereignty in 1898, the arsenal was the last site held by Spanish troops, who used it as a headquarters during the process of repatriation. Once this process was complete, the structure was handed over to the government of the United States, which in turn gave the local government permission to use it for governmental offices. Today, the former Navy Arsenal belongs to the Institute of Puerto Rican Culture, which has its offices in the complex, along with governmental administrative offices and exhibition rooms.
–Excerpted from Enciclopedia Puerto Rico: https://enciclopediapr.org/en/encyclopedia/san-juan-old-navy-arsenal/