The cathedral sits on the highest ground in Porto's historic center, built on the site of a chapel founded by Henry of Burgundy, Count of Portugal, and his wife in 1108. A pre-Romanesque church already stood here when crusaders passed through in 1147, as recorded in the chronicle De Expugnatione Lyxbonensi. Construction of the present building began in the second half of the 12th century and continued into the 16th. The result is a fortress-church: two square towers flanking a facade under crenellated arches, giving the building the look of a castle as much as a cathedral. The Romanesque rose window survives between later Baroque additions, a circle of medieval stonework framed by 18th-century elaboration. Inside, the narrow nave is covered by barrel vaulting, its stone roof supported by flying buttresses -- one of the earliest uses of this technique in Portugal.

Around 1333, a Gothic funerary chapel was added for Joao Gordo, a Knight Hospitaller who served King Dinis I. His tomb bears a recumbent figure surrounded by relief carvings of the Apostles, a quiet masterpiece of medieval Portuguese sculpture. The Gothic cloister, built between the 14th and 15th centuries, witnessed one of Porto's most consequential events: in 1387, King John I married the English Princess Philippa of Lancaster here, an alliance that would produce a remarkable generation of sons including Prince Henry the Navigator. The marriage cemented the Anglo-Portuguese alliance, the oldest in the world still in force, and the cathedral where it took place remained the spiritual heart of a city that would help launch the Age of Discovery.

The cathedral's exterior changed dramatically in the Baroque era. In 1736, the Italian architect Nicolau Nasoni added an elegant loggia to the lateral facade, introducing curves and ornamentation to a building originally designed for austerity. By 1772, the main Romanesque portal had been replaced and the tower cupolas altered. Inside, the transformation was even more thorough. A magnificent silver altarpiece, crafted by Portuguese artists in the second half of the 17th century, fills one chapel. The original Romanesque apse with its ambulatory was demolished and rebuilt in Baroque style, then decorated with wall paintings by Nasoni and new choir stalls. Between 1727 and 1729, Santos Pacheco designed and Miguel Francisco da Silva executed the main chapel's altarpiece, depicting scenes from the Song of Songs. The terrace cloisters received azulejo tile panels by Antonio Vidal, while Pachini painted allegories of moral values on the coffered ceiling of the chapter house in 1737.

Walk through Porto Cathedral and you walk through Portugal's architectural history in compressed form. Romanesque severity gives way to Gothic delicacy, which yields to Baroque excess, which coexists with 20th-century restorations. The few sarcophagi in the remnants of the Early-Romanesque ambulatory are the oldest survivors, their stone darkened by centuries. Mass is still celebrated daily at eleven in the morning, the liturgy continuing in a space that has hosted worship since before Portugal existed as an independent nation. The cathedral is not Porto's most beautiful building -- it is too architecturally heterogeneous for that, a word the guidebooks use diplomatically -- but it is the most layered, each era of the city visible in its stones and tiles and gilding.