This study integrates bone collagen stable isotope data (carbon, nitrogen and sulphur) from 33 human adult tibiae (15 females; 18 males) and 13 faunal remains from Tomar, while it was under the Military Orders domain (eleventh-seventeenth centuries). Historical literature indicates that the amount of meat consumption amongst Templars was lower than in individuals with similar social status. In Medieval times, these Military Orders had total control of towns and angling and fishing rights, but their influence on the general population diet remains unknown. While no statistically significant differences (p > 0.05) were found between sexes, social status, or for bone collagen δ 13 C and δ
34Sbetween age groups, δ 15 N did differ significantly with age, which may be related to tooth loss in old individuals. Additionally, the human samples have higher stable isotope differences, in comparison with faunal samples, than would be expected within the food web, particularly for δ 13 C. This human bone collagen δ 13 C enrichment may reflect a diet rich in aquatic protein intake, which is also supported by δ 34 S archived in human and faunal samples, and the presence of oysters and cockles shells at the excavation. The religious diet restrictions might have led to a higher intake of aquatic protein when meat consumption was not allowed.