Between the 16th and 20th cen­turies, a series of defen­sive struc­tures was built at this strate­gic point in the Caribbean Sea to pro­tect the city and the Bay of San Juan. They rep­re­sent a fine dis­play of Euro­pean mil­i­tary archi­tec­ture adapt­ed to har­bour sites on the Amer­i­can con­ti­nent.