Shrouded in history: Unveiling the ways of life of an early Muslim population in Santarém, Portugal (8th- 10th century AD)

Abstract

In around 716 AD, the city of Santarém, Portugal, was conquered by the Berber and Arab armies that swept the Iberian Peninsula and went on to rule the region until the 12th century. Archaeological excavations in 2007/08 discovered an Islamic necropolis (Avenida 5 de Outubro #2-8) that appears to contain the remains of an early Muslim population in Santarém (8th- 10th century). In this study, skeletal material from 58 adult individuals was analysed for stable carbon (δ13Ccol; δ13Cap), nitrogen (δ15N) and sulphur (δ34S) isotope ratios in bones, and stable oxygen (δ18O), carbon (δ13Cen) and radiogenic strontium (87Sr/86Sr) isotopes in tooth enamel. The results of this study revealed a dietary pattern of predominantly C3-plant and domestic C3-fed herbivore consumption during adulthood (δ13Ccol and δ15N, respectively) but a higher proportion of C4-plant input during childhood (δ13Cen) for some individuals-interpreted as possible childhood consumption of millet porridge, a common practice in North Africa-in those with unorthodox burial types (Groups 1 and 2) that was not practiced in the individuals with canonical burials (Group 3). In this first mobility study of a medieval Muslim population in Portugal, δ18ODW values revealed greater heterogeneity in Groups 1 and 2, consistent with diverse origins, some in more humid regions than Santarém when compared to regional precipitation δ18O data, contrasting the more homogenous Group 3, consistent with the local precipitation δ18O range. Ancient DNA analysis conducted on three individuals revealed maternal (mtDNA) and paternal (Y-chromosome) lineages compatible with a North African origin for (at least) some of the individuals. Additionally, mobility of females in this population was higher than males, potentially resulting from a patrilocal social system, practiced in Berber and Arab communities. These results serve to offer a more detailed insight into the ancestry and cultural practices of early Muslim populations in Iberia.

Fig 1

Map of a.) Location of Santarém and b.) Excavated area of Avenida 5 de Outubro. Map in Fig 1A). drawn by MacRoberts RA and adapted from Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Portugal-CIA_WFB_Map.png), CC public domain. Map in Fig 1B.) taken from openstreetmap.org licensed under the Open Data Commons Open Database Licence (ODbL).

Fig 2. Geological map of Santarém and sampled sites for bioavailable ⁸⁷Sr/⁸⁶Sr baseline.

Map drawn by MacRoberts RA and adapted from the LNEG (Laboratório Nacional de Energia e Geologia) 1: 50 000 geological raster maps “31-A” and “31-C”. (https://geoportal.lneg.pt/pt/dados_abertos/cartografia_geologica/cgp50k/) [67]. Both geological raster maps 31-A and 31-C are published under CC By 4.0. (31-A: https://sig.lneg.pt/metadados/catalog/search/resource/details.page?uuid=831fb1df-e743-4e23-97d0-91af58d46f02; 31-C: https://sig.lneg.pt/metadados/catalog/search/resource/details.page?uuid=20486b7f-20be-4506-aa88-5caacc5d6946).

Fig 3. Image of intersecting graves 955 and 956 with differing orientations.

Republished from [91] under a CC BY license, with permission from Medievalista, original copyright 2012.

Fig 4. Grave orientation classification, diagram showing the direction that skeletons would face in right lateral position with faces turned towards the east or southeast, and the direction from Santarém towards Mecca.

Drawn by MacRoberts RA. The map image inset was obtained from Wikimedia Commons (https://commons.wikimedia.org/wiki/File:North_Africa_location_map.svg), CC public domain. The skeletons were adapted from [91] with permission from Medievalista, original copyright 2012, republished under a CC BY license.

Fig 5. Map of Avenida 5 de Outubro necropolis showing position of graves and Bar graph showing # of individuals per group (inset).

Fig 6. Human and fauna δ¹⁵N and δ¹³C_col.

Squares represent expected range of +1 trophic level (+0–2‰ in δ¹³C_col; +3–5‰ in δ¹⁵N) increase over mean Bos and Ovicaprid values, respectively.

Fig 7. Human δ¹³C_col and δ¹³C_ap plotted against regression lines [131] indicating main protein and energy sources in diet.

Fig 8. Human and fauna δ³⁴S and δ¹³C.

Fig 9. Human ⁸⁷Sr^/86Sr results compared to bioavailable ⁸⁷Sr^/86Sr for Santarém (plant ash samples from this study and [61].

Fig 10

Human (a.) bone collagen (δ¹³C_col) vs bone apatite (δ¹³C_ap) and (b.) bone collagen (δ¹³C_col) vs tooth enamel (δ¹³C_en), by grave orientation (plotted against C₃ protein regression line [131] indicating main protein and energy sources in diet).

Fig 11. Isotope results according to grave orientation.

a.)δ¹³C_col, b.) δ¹⁵N, c.) δ³⁴S, d.) δ¹³C_en, e.) δ¹⁸O_DW and f.) ⁸⁷Sr/⁸⁶Sr. M1 teeth are indicated by triangles in 9e.

Fig 12. Human and fauna δ³⁴S from Santarém (this study), Évora [22] and Tomar[19] along with expected regional range [47].

Fig 13. Human and fauna δ¹⁵N and δ¹³C_col by sex.

Squares represent expected range of +1 trophic level increase (+0–2‰ in δ¹³C_col; +3–5‰ in δ¹⁵N) over mean Bos and Ovicaprid values, respectively.

Fig 14. Human δ¹⁸O_DW with multi-tooth comparison.

Individuals with values outside of local range and/or of whom multiple teeth were sampled are in colour and labeled. Individuals within local range and with only one tooth sampled are in grey. Solid triangles = M1s, circles = M2s, squares = M3s, cross = PM1 and diamond = PM2. Hollow triangles represent hypothetical M1 values corrected (-1‰ from δ¹⁸O_c VPDB) for breastfeeding.

Fig 15. Human ⁸⁷Sr^/86Sr results by sex compared to bioavailable ⁸⁷Sr^/86Sr for Santarém (plant ash samples from this study and James et al.

2022 [61]).

Fig 16. Human ⁸⁷Sr^/86Sr and δ¹⁸O_DW results by sex.

Grey lines indicate the limit of the expected ‘local’ range for the respective isotopes in Santarém. For ⁸⁷Sr^/86Sr, bioavailable range is determined from plant ash samples from this study and James et al. 2022 [61].