The hill of São Jorge Castle has commanded the Tagus estuary since antiquity. Archaeology has revealed Iron Age settlement and later Roman, Visigothic, and Islamic occupation. By the mid-eleventh century, when Lisbon was an important Muslim city known as al-Ushbuna, a fortified citadel and elite residential quarter occupied the summit. Walls protected the ruling center and connected with broader urban defenses descending toward the river. The surviving castle reflects this layered landscape rather than a single founding moment.

In 1147 Afonso Henriques, the first king of Portugal, besieged Lisbon with the assistance of northern European crusaders traveling toward the eastern Mediterranean. After months of fighting and negotiation, Muslim defenders surrendered on October 25. The conquest brought killing, displacement, religious conversion, and redistribution of property as Christian rule replaced Islamic government. The legend of Martim Moniz sacrificing himself in a gateway became a patriotic story, but its historical basis is uncertain. The capture gave the Portuguese monarchy a major Atlantic port.

Lisbon became the kingdom’s capital in the thirteenth century, and the citadel developed into the royal Alcáçova palace. Kings rebuilt halls, towers, chapels, and defenses; court ceremonies and administration occupied the hill. Ferdinand I’s new city wall of 1373–75 expanded protection around growing neighborhoods. The castle resisted Castilian pressure during the crisis of 1383–85. Under John I it gained its dedication to Saint George, reflecting both royal warrior symbolism and the king’s English alliance through Philippa of Lancaster.

The palace received returning navigator Vasco da Gama in 1499 and hosted court entertainments, but royal life shifted to the new Ribeira Palace beside the river during the sixteenth century. The old complex became a barracks, prison, hospital, archive, and institutional space. Earthquakes in 1531 and especially 1755 caused severe destruction. After the 1755 disaster, military and charitable uses filled surviving buildings while ruins and later construction obscured the medieval plan.

During the authoritarian Estado Novo, a major restoration campaign from the late 1930s through the 1940s demolished many post-medieval structures and reconstructed battlements to create a powerful image of the nation’s medieval origins. Archaeology has since complicated that nationalist presentation by uncovering Islamic residences and earlier occupation. The castle opened as a monument and museum with broad views over Lisbon. Its history includes conquest and coexistence, monarchy, maritime expansion, earthquake, military reuse, and politically motivated restoration. Visitors encounter genuine medieval walls, archaeological remains, and twentieth-century reconstruction together; understanding the differences is essential to reading the castle as evidence rather than timeless national scenery.

Archaeology within the castle has continued to refine this long sequence, identifying Islamic neighborhoods, earlier occupation, palace remains, cisterns, and changes in the walls. The site’s commanding views helped make it an emblem of Lisbon, but they can also flatten conflict into panorama. Muslim residents expelled or displaced after 1147, enslaved people and servants of the royal household, soldiers, prisoners, and working families all participated in the hill’s history. Present interpretation combines excavated remains with heavily restored battlements. Castelo de São Jorge is consequently both an authentic archaeological landscape and a twentieth-century national monument, shaped as much by decisions about demolition and reconstruction as by medieval warfare and royal ceremony.