Santiago de Compostela developed around a tomb identified in the early ninth century as that of the apostle James the Greater. According to medieval tradition, a hermit observed miraculous lights and alerted Bishop Theodemir of Iria Flavia, who recognized the burial. King Alfonso II of Asturias supported a shrine and became associated with the earliest pilgrimage route. The historical basis for the apostle's presence in Galicia remains a matter of faith and debate, but belief in the relics created one of medieval Europe's most influential sacred destinations.

Successive churches served the growing pilgrimage. Forces under al-Mansur attacked Compostela in 997 and destroyed the basilica, though the shrine survived or was soon restored. Construction of the present Romanesque cathedral began in 1075 under Bishop Diego Peláez and King Alfonso VI. Work continued under Archbishop Diego Gelmírez, who promoted Santiago's ecclesiastical status, infrastructure, and international connections. Builders organized a large cruciform church with ambulatories and radiating chapels that allowed crowds to move around the apostolic tomb while worship continued at the main altar.

Pilgrims traveled through networks now called the Camino de Santiago, following several routes across Iberia and Europe. Roads, bridges, hospitals, monasteries, markets, and towns grew to serve them. The Codex Calixtinus assembled liturgy, miracle stories, sermons, music, and a famous twelfth-century guide to the journey. At the cathedral's western entrance, Master Mateo created the Pórtico da Gloria from the late 1160s, combining architecture and sculpture in a vision of judgment and heavenly worship. Pilgrimage also carried disease, crime, commerce, languages, and artistic ideas, not only devotion.

Gothic, Renaissance, and Baroque patrons continually altered the cathedral and surrounding squares. The medieval west front was enclosed behind Fernando de Casas Novoa's soaring Obradoiro façade in the eighteenth century, while the Clock Tower and other elevations reshaped the skyline. Convents, colleges, canons' houses, civic buildings, and narrow streets turned the shrine into a complex city. The cathedral's great censer, the Botafumeiro, became a celebrated ritual object. Santiago also served archbishops and political rulers who used the apostle's image to support warfare, monarchy, and competing ideas of Spanish identity.

Pilgrimage declined in parts of the early modern and modern periods, and the relics were hidden in the sixteenth century for fear of attack. Their nineteenth-century rediscovery and papal recognition encouraged renewed visitation. Twentieth-century scholarship, road travel, heritage programs, and European cultural initiatives revived the Camino on a much larger scale. Under Francisco Franco, official ceremonies appropriated Saint James for nationalist Catholicism; democratic Spain and Galicia later promoted more plural religious, cultural, and recreational meanings. Mass participation now supports communities but strains housing, paths, and sacred space.

UNESCO inscribed Santiago's Old Town in 1985, recognizing the cathedral and the Romanesque, Gothic, Renaissance, and Baroque city around it. Conservation has cleaned façades, stabilized sculpture, managed moisture, and restored the colored surfaces of the Pórtico da Gloria. The cathedral remains an active shrine, not merely the finish line of a tourist route. Its importance lies in the enduring interaction of belief and movement: an uncertain ancient tradition generated architecture, music, urban growth, hospitality, political symbolism, and personal journeys that continue to remake both the city and the meaning of pilgrimage.