O'Reilly and O'Daly, 1765-1790

In 1762 the British took Havana. Madrid looked at every Caribbean plaza and found it lacking. The crown sent Field Marshal Alejandro O'Reilly, an Irishman in Spain's service, to inspect Puerto Rico in 1765, and with him Colonel Tomás O'Daly as chief engineer. The National Park Service names both on El Morro's history page. O'Reilly was to reform the troops. O'Daly was to reform the walls.

What one walks at El Morro is mostly their century, not the tower of 1539. The NPS's language is that the standing work belongs largely to 1770-1790. O'Daly raised the land fronts, thickened batteries, and finished the six-level mass in time for the British return of 1797. At San Cristóbal, he and Juan Francisco Mestre pushed the Vaubanesque outer works that turn a hill battery into a deep fortress. The Irish names in Spanish payroll books are not a curiosity. Catholic Ireland sent professional soldiers to Bourbon Spain; the Caribbean received their drawings.

O'Reilly's inspection was a troops paper as much as a stone paper. Militias were counted, veterans reorganized, and San Juan graded as a first-rate defense. The money still came as the situado. The difference after 1765 is that the subsidy was spent on a plan and not on patches. When Abercromby came in 1797, he found a finished system, not a medieval donjon. The drill on El Morro's and San Cristóbal's plazas is part of that file: men trained for the new walls, not just walls drawn for missing men.

A hundred years later the same walls would look old against breech-loading naval guns. That is 1898, and it does not cancel 1765. Each year on this board has its own weapons. O'Reilly and O'Daly built for sail fleets and for infantry. On those terms, they succeeded.

Remember the sequence. Havana falls. An Irish field marshal writes a report. An Irish engineer stays. The profile of Old San Juan, the one on every postcard, is that stay. The date 1539 is a founding. The O'Daly date is the building.

Sources: NPS El Morro. Freeze 2026-08-22.