El Morro is one of two forts inside the San Juan National Historic Site. Its sister, the Fort San Cristóbal, is one of the largest Spanish fortresses in the Americas. The site is open from 9 a.m ...

In 1539, the Spanish began building a fort in San Juan to fend off attacks from European rivals. The fort was known as "El Morro," and as the attacks on it multiplied, so too did its defenses.