Why It Took 251 Years to Finish a Single Fort
Castillo San Felipe del Morro, known as El Morro, was built in phases across 251 years, from 1539 to 1790, though construction in earnest began in 1589 using plans by Juan de Tejeda and Juan Antonelli, employing over 150 enslaved laborers and dozens of skilled workers. Named for King Philip II, it evolved from a simple promontory position with a single cannon into a six-level military stronghold. Its thick walls repelled attacks by Sir Francis Drake and other famous military leaders, though the English briefly captured it in 1598 by landing troops on land rather than attacking from the sea.
Why 251 years of construction reflects genuinely evolving military needs
Rather than a single building project, the fort's growth from one cannon position to a six-level stronghold was a gradual response to changing threats over two and a half centuries, not an unusually slow construction timeline.
Why the fort's defenders held off Sir Francis Drake, but not everyone
The thick walls genuinely repelled Drake's attack, but there's an honest exception: English forces did briefly capture the fort in 1598, not by attacking from the sea, but by landing troops on land instead.
Why enslaved laborers' documented role matters for understanding the fort's construction
Over 150 enslaved workers built the fort alongside Spanish engineers and soldiers, a documented labor history that's part of the fort's story, not a detail to leave out.
What This Means for Planning a Visit
The practical takeaway is that most of what stands today actually dates from construction in the late 1700s, not the original 1539 structure, worth understanding this before assuming every visible wall is centuries older than it actually is. San Juan's own practical visiting details are covered on the city's main page.