Santiago de Compostela is, together with Rome and Jerusalem, one of the three main pilgrimage and religious centres for Catholicism. The belief that the remains of St James the Great, one of the twelve apostles of Jesus Christ, is buried there has stimulated, since their reported discovery in the 9th century AD, a significant flow of people from across the European continent and beyond. Little is known about the practical experiences of people living within the city during its rise to prominence, however. Here, for the first time, we combine multi-isotope analysis (δ13C, δ15N, δ18Oap, δ13Cap and 87Sr/86Sr) and radiocarbon dating (14C) of human remains discovered at the crypt of the Cathedral of Santiago to directly study changes in diet and mobility during the first three centuries of Santiago’s emergence as an urban centre (9th–12th centuries AD). Together with assessment of the existing archaeological data, our radiocarbon chronology broadly confirms historical tradition regarding the first occupation of the site. Isotopic analyses reveal that the foundation of the religious site attracted migrants from the wider region of the northwest corner of the Iberian Peninsula, and possibly from further afield. Stable isotope analysis of collagen, together with information on tomb typology and location, indicates that the inhabitants of the city experienced increasing socioeconomic diversity as it became wealthier as the hub of a wide network of pilgrimage. Our research represents the potential of multidisciplinary analyses to reveal insights into the origins and impacts of the emergence of early pilgrimage centres on the diets and status of communities within Christian mediaeval Europe and beyond.

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