La Fortaleza and San Juan National Historic Site in Puerto Rico

During the 16th century, recognizing the need to protect the Spanish treasure fleets on their voyages to and from the New World, the Spanish erected vast fortifications throughout their territories in the Caribbean Islands and the Gulf of Mexico. The Spanish system of fortifications in San Juan, Puerto Rico is the oldest European construction in the United States and one of the oldest in the New World. These fortifications guarded the entrance to San Juan Bay, helped the Spanish maintain sovereignty over Puerto Rico, and protected Spanish commerce in the Caribbean basin. The forts and three miles of city wall are fine examples of military architecture reflecting the power and glory of the Spanish Empire, and the beginning of European ascendancy in world affairs.