Mobility of populations in the transition from Muslim world to Portuguese Kingdom in the Algarve, South Portugal, 11th-13th centuries

Abstract: This study investigates mobility during the transition from Muslim to Christian rule in the Algarve, southern Portugal (11th–13th centuries), using multi-isotope analysis to understand population dynamics during this complex conquest period. Skeletal remains from two key populations were analysed: the final Muslims buried in Loulé before the Christian conquest (necropolises of Quinta da Boavista and Hospital da Misericórdia) and the earliest Christians buried in Cacela-a-Velha following the Order of Santiago’s capture in 1240 (necropolis of Poço Antigo). Contemporary faunal remains from trash pits and storage silos were also examined (Loulé: Oficina do Senhor Carrilho; Cacela: Silo 7 of Largo da Fortaleza). Strontium, oxygen, and sulphur isotope analysis of human and animal remains were combined with plant sampling for environmental baselines. Machine learning algorithms integrated this data with published Iberian Peninsula plant isotope ratios to create updated strontium isoscape maps, enabling probabilistic geographic assignment of non-local individuals. Ancient DNA analysis of selected Muslim individuals provided additional mobility insights. Results reveal strikingly different mobility patterns. Muslim individuals were largely local (~ 95%) with a few non-local likely from the Maghreb or eastern Spain. Conversely, the Christian population displayed extensive mobility, greater for males than females, with nearly 50% non-local to the Algarve. Potential origins were diverse and included regions along the Guadiana River and N/NE areas. While Muslims showed no sex-based isotope mobility patterns, paleogenetic analysis suggested patrilocal social structures and highlight the complex genetic landscape of the region. The overall data showcase a colonisation process poorly documented in other sources.