Porto Cathedral (Sé do Porto)

Porto Cathedral, the Sé do Porto, was built beginning in the 12th century as a fortified church on the hilltop above the Douro river, its thick granite walls and crenellations reflecting the building's original dual role as both a place of worship and a defensive structure during the Christian Reconquista. The Romanesque core survives most clearly in the rose window and the heavy nave walls, while a 14th-century Gothic cloister, decorated with 18th-century azulejo tile panels depicting the life of the Virgin and Ovid's Metamorphoses, was added later, and the west front received a Baroque remodeling in the 18th century under architect Nicolau Nasoni, who also added the loggia and monumental staircase in the adjoining episcopal palace. The cathedral is where King João I married Philippa of Lancaster in 1387, an alliance that sealed the Anglo-Portuguese Treaty of Windsor, the oldest diplomatic alliance still in force in the world. Inside, visitors can see a solid silver altarpiece in the Chapel of the Blessed Sacrament, largely spared from Napoleonic troops' looting during the Peninsular War because it had been painted over to disguise its value, and a Gothic tomb attributed to João Gordo. Presentation moves visitors from the fortified nave through the cloister's tiled galleries to the upper-floor chapter room, tracing the building's shift from Romanesque fortress-church to Baroque ecclesiastical showpiece. The cathedral sits within Porto's UNESCO-listed historic centre and anchors the upper old town above the Ribeira district.