Diet in Medieval Portugal: exploring inter-faith and social dynamics through stable isotope analysis

Medieval Portugal, tucked between a Christian north and an Islamic south, and at a crossroad
between Africa and Europe, saw the birth and development of a multi-faith and multi-cultural
society. Muslims and Christians co-existed in this region, shaping a unique pluralistic society, first
under Islamic political control and later under Christian rule following the Christian conquest of the
12th century. This thesis applies carbon (δ13C) and nitrogen (δ15N) isotope analysis to characterises
early and late medieval diet under Islamic (8th-12th) and Christian rule (12th-15th), exploring the
impact of a shifting political system, status and faith onto economy, food availability and
consumption.
Analysis of stable isotopes of carbon (δ13C) and nitrogen (δ15N) was performed on bone collagen
from 176 animals and 251 humans including Muslims and Christians sampled from sites covering a
north-south trajectory (Laranjal, Coimbra, Lisbon, Setubal, Beja, Silves and Loulé) with a date range
between the 8th and 15th centuries. Results indicate that a faith-related difference in diet exists but
is also related to chronology and geographical location. Early medieval Muslim diet is based on
animal protein and C3 plants with possible inputs of low trophic level fish in Setubal and Loulé; while
bigger proportions of marine fish appear in the diet of late medieval Muslims in Lisbon. Early
medieval Christian diet is based on terrestrial resources with a reliance on C4 plants in Coimbra;
while late medieval Christian sites in southern Portugal show a reliance on marine resources.
Results show a difference in diet between early and late medieval sites with a clear change in
economy possibly brought about by the Christian conquest. Multi-faith sites (Lisbon, Beja and
Silves) show an increment of at least 11% in the quantity of marine protein included in the human
diet of Muslims and Christians from the early to the late medieval period.