Diet and mobility during the Christian conquest of Iberia: the multi-isotopic investigation of a 12th–13th century military order in Évora, Portugal

The Kingdom of Portugal was established with the help of military-monastic orders, which provided important defence against Muslim armies during the 12th–13th century Christian conquest. While historical sources document the main events of this period, this research seeks to elucidate individual lifestyles and movement, aspects typically absent from written records. A multi-isotopic approach was used on skeletal material from eight Christian and two Muslim burials from Évora, Portugal (11th–13th centuries). Anthropological and archaeological evidence suggests the Christian adults belonged to the Évora Militia, which we seek to confirm through the reconstructed diet and mobility of these individuals. Stable carbon, nitrogen and sulphur isotopes were measured in bone collagen, and radiogenic strontium, carbonate stable oxygen and apatite stable carbon isotopes were measured in tooth enamel. Results of the stable oxygen and radiogenic strontium isotopes indicated diverse origins of the Christian population, while at least one individual was local. The Muslim adult was local, as anticipated. The δ13Cen (enamel) values provide evidence of childhood consumption of different cereals (C3 and C4), possibly linked to social status. The δ13Ccol (bone collagen) human values indicated mostly C3 diets with varying inputs of C4, while δ15N reflected high protein intake overall. The mean diet-consumer spacing of this population was compared to other isotopic studies from Medieval Iberia and other European monastic/convent populations. A visible trend emerged in populations that likely followed religious fasting rules, including the Évora Christians. The results of this study indicate that the Order of Évora was composed of members from diverse geographic and possibly social origins, an aspect previously unclear in written sources.