San Juan, founded by Spanish colonists in 1521, is the oldest city under the United States flag and one of the oldest continuously inhabited European settlements in the Americas, its historic district, Old San Juan, retaining street layouts and fortifications largely unchanged since the Spanish colonial era. The city’s massive fort, Castillo San Felipe del Morro, took roughly 250 years to complete in its final form, its walls reaching up to 12 metres thick in places, designed to withstand not just cannon fire but centuries of attempted sieges from rival European powers and pirates alike.

That fortification effort worked remarkably well, San Juan successfully repelled attacks from Sir Francis Drake in 1595 and a determined Dutch siege in 1625, among others, a defensive record that made it one of the most strategically vital, and most heavily defended, ports in the entire Spanish colonial empire.

Streets Paved With Blue Cobblestones From Spain

Many of Old San Juan’s streets are paved with adoquines, distinctive blue-grey cobblestones made from smelted iron slag, originally shipped from Spain as ballast in colonial cargo ships, similar in origin to Savannah’s ballast stones halfway around the world, and repurposed for paving once the ships had unloaded their actual cargo. Puerto Rico’s political status remains a genuinely unresolved and actively debated question, a US territory rather than a state, its residents US citizens who nonetheless cannot vote in presidential elections while living on the island, a tension frequently discussed alongside the historic fortress walls surrounding it.

The colourful, tightly packed colonial buildings throughout Old San Juan, many now housing shops, restaurants, and galleries, remain protected under strict historic preservation regulations, keeping the district’s Spanish colonial character intact even as the surrounding modern city has grown substantially around it.

Painting Fortress Walls Against the Caribbean

El Morro’s massive stone walls against deep Caribbean blue give a watercolourist dramatic scale and historic weight to work with. We’ve captured that fortress presence in our own San Juan Watercolor Print, painted first by hand and printed to order on archival paper, a small piece of Puerto Rico for a wall at home.

Built to repel some of history’s most determined sieges and never once successfully taken by force, San Juan’s fortress walls remain standing largely because they simply did exactly what they were built to do.