This six-level fortress was continually enlarged in the seventeenth and eighteenth centuries because it was in constant danger of English, Dutch, and French attack. Deep in one of the bombproof vaults is a museum with displays illustrating El Morro's history. The fortress San Cristobal is even larger than El Morro. Begun in 1634, San Cristobal protected the land approaches to old San Juan. Today its high bastions still loom over its nearest neighbor, the beautiful Capitol of Puerto Rico.
Visitors can see a restored eighteenth-century Spanish troop quarter inside one of the vaults.