Castillo San Felipe del Morro is beautiful. You can understand why it’s the bright star of San Juan tourism. But it was built as a killer.
Spain built it in the early 1500s to protect their utter dominance in the Caribbean—and for nearly 400 years, it did. Sitting atop a rocky headland at the entrance to San Juan Bay, El Morro was a weaponized welcome mat. Anyone arriving by sea for trade, colonization, or war had to pass it. Most did not.
Back then, Spain had a chokehold on the Western Hemisphere, and they zealously guarded their advantage against the Dutch, the French, and eventually the British. And even though it might be hard to understand how one small island plays into that, it does. Puerto Rico isn’t just an isolated, beach-ringed paradise (well, it is, of course—but there’s more to it). It’s also perfectly positioned to control shipping in the region.
Imagine it as the narrowest point in the funnel that leads you from the Atlantic into the Gulf of Mexico and the Caribbean Sea. Getting anywhere in the area—from Havana to Veracruz to Cartagena—meant passing Puerto Rico. And everybody wanted in. To get their beak wet on the riches pouring out of the Americas by the shipload.
And the Spaniards who first planted the imperial flag here knew it. One of their first priorities was to build El Morro. They started in 1539 and just kept going, reinforcing and enlarging it for centuries. Puerto Rico—and El Morro—became the front line of Spain’s transatlantic empire.
Their zeal was only strengthened by the national belief that Spain was the Vatican's personal security detail. By the mid-1500s, Protestant reformers were gaining ground across Europe—England had split, the Dutch were rebelling, and France was wobbling between Catholic kings and Huguenot nobles. Spain saw itself as the last righteous monarchy standing. Which meant they deserved all the gold, tobacco, and chocolate in the New World? They thought so. Protecting trade routes may have been the first priority, but defending the faith was a close second. El Morro wasn't just a fortress—it was a sermon in stone. "Oh no, you don't. Not today, heretics."
Most got the message. But the Dutch tested it in 1625. They attacked from the south, bypassing El Morro's fearsome seaward defenses and burning San Juan to the ground. El Morro held, but barely. The island's leaders had holed up inside and launched harrying raids for weeks until the Dutch finally gave up and left. It wasn't quite a conquest—but it was deeply embarrassing.
Spain responded by building up the city's landward side, eventually constructing Castillo San Cristóbal and turning Old San Juan into a walled compound. Still, El Morro remained the big gun, trained at the horizon.
El Morro was repaired, reinforced, and left to glower at the sea for another 250 years. And it still does. You can feel the tension baked into its stone—the kind that assumes an enemy is always coming and never politely. Powder magazines. Sentry towers. Ramparts thick enough to ride out a dayslong cannon barrage. Stairwells tight as corkscrews to slow down invaders or trap smoke. There's no wasted space. Everything here has a purpose, and none of it is decorative.
Except maybe the lighthouse.
The first version went up in 1846 under Spanish rule. The one standing now came later—built in 1908 by the U.S. military, boxy and black-and-white like it was designed by a federal office supply clerk. It's the only lighthouse in the National Park system with that color scheme. And the only one, probably, that was once part of an active artillery installation.
Because, yes, the Americans took over. In 1898, after the Spanish-American War, Puerto Rico changed hands, and El Morro was absorbed into Fort Brooke—a sprawling U.S. Army base that swallowed most of the open green space behind the fort. It was paved, wired, and armed with new defenses for both World Wars. At one point, concrete bunkers were carved into the old stone walls—scars still visible today.
The sprawl of Fort Brooke nearly buried El Morro beneath 20th-century infrastructure. But by the 1960s, the Army pulled out, as the fort’s strategic value faded, and budgets shifted elsewhere. The National Park Service took over, and restoration work began. In 1983, El Morro and the surrounding city walls were designated a UNESCO World Heritage Site.
I visited on a weekday afternoon. The weather was perfect. The lawn was full of kids flying kites and couples posing for selfies. Inside, it was crowded but not unmanageable. I kept climbing. Up ramparts. Down tunnels. Around spiraling stairs. I’d seen Castillo San Cristóbal earlier that morning, and while it felt vast and underappreciated, El Morro felt…inevitable.
It’s not the scrappy sibling. It’s the reason San Juan exists at all. If you only have time for one fort, this is the one. Just don’t confuse the photo ops for softness. El Morro may be scenic, but it was built to destroy.
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