Case Study: Dietary Isotope Analysis at Portmahomack

Dr Shirley Curtis-Summers

University of Bradford

In 1994, archaeological investigations began at the old Tarbat Parish Church in Portmahomack, Easter Ross (MHG8473) that would last for over 12 years and become known as the first excavated Pictish monastery in Scotland. Excavations unearthed a wealth of discoveries including Pictish sculpture, beads, moulds, glass, vellum pebbles, animal bones, the list goes on. Also found were human skeletons dating from the 6th to 17th centuries AD, presenting the potential to reconstruct hundreds of years of Highland history through archaeological scientific techniques. 

Dr Curtis-Summers assessing one of the Portmahomack skulls.  

Original osteological assessments were carried out in 2000 (King 2000) and updated recently by Dr Shirley Curtis-Summers as part of a large-scale study on diet and health at Portmahomack (Curtis-Summers 2015; King and Curtis-Summers 2016). As part of this study, stable carbon and nitrogen isotope analysis was carried out on human bone collagen from 178 adult and child skeletons to reconstruct their diets. This type of isotope analysis on bone may reflect diet from around the last 5 years of life in children or the last 20 years of life in adults, although variation occurs due to the type of bone analysed and the age of the individual at death. Generally, we can reconstruct whether an individual ate a lot of meat or fish and whether they were local to their place of burial. The different types of tissue studied (eg bone or teeth) and the species of isotopes analysed will determine the type of data and information obtained (ScARF Science Section 2.4 Isotope Analysis). For example, carbon and nitrogen isotope values can provide evidence of dietary protein consumption by humans and animals while strontium and oxygen isotope analysis, which are influenced by the consumption of plants and drinking water, can identify whether individuals lived near or far away from their site of burial. Sulphur isotope analysis can tell us about both diet and mobility, plus its isotopic ratios in bone collagen represents uptake from plants and soil of a particular area.  Recently, new isotope methods focussing on the analysis of teeth have been developed to give a much finer snapshot of diet (Beaumont et al 2018). Because teeth grow incrementally (in layers) and at different stages during childhood, scientists can analyse sections of a tooth and reconstruct diets from in utero (foetuses) to early adulthood, depending on what tooth is analysed. Knowing the dietary history of an individual offers an important component in building a biological profile of a deceased individual, or in the case of Portmahomack, a whole skeletal assemblage.

One of the skeletons being excavated at Portmahomack (c) Tarbet Discovery Program

The results from stable isotope analysis at Portmahomack revealed a stark difference in the diets of the early Pictish communities, compared to the later parish church community. It was discovered that the early medieval Picts were predominantly beef eaters and did not eat fish, yet by the later medieval period, the parish church community had a predominantly fishy diet. This contrasts with what is often seen in later medieval monastic communities, where fish consumption connected to fasting practices was the norm. Dietary differences were also identified between different sex and age groups at Portmahomack, which may reflect gendered divisions in labour and one’s status within the family unit. 

As well as the use of cattle for meat, their bones and hides were also an important by-product used to make vellum at the Pictish monastery (Carver and Spall 2004). Other finds such as a bone stylus, metal moulds, crucibles and evidence of gold recycling suggests the monks at Portmahomack were also gilding mercury, most likely to decorate their holy books with gold leaf. This evidence of bookmaking and scribing therefore suggests the presence of an early Christian literate community during the monastic phase at Portmahomack (Case Study: Portmahomack; HighARF Chapter 8.5). 

Artist impression of the monastery at Portmahomack (c) John Tosca 

This is the first large-scale study on the Portmahomack skeletal assemblage which gives much needed insights into Pictish and medieval subsistence patterns. It also provides interpretation of the social and religious influences that could impact diet over time (Curtis-Summers et al 2020). Other isotope studies have produced data to suggest similar dietary patterns, from comparable sites such as Lundin Links (Fife), Westness (Orkney), and most recently, the Bridge of Tilt (Modzelewski 2008, Berret and Richards 2004, Czére et al 2021). However, the opposite has been found at other sites, such as Newark Bay (Orkney) where the community appear to have had a continuously fishy diet (Richards et al. 2006). These cases tell us that there was variation in Pictish diet across the country, which appears to be not just influenced by location, resources, and seasonality, but by social, economic, and religious influences on the types of food consumed. 

New isotope analysis is planned and will contribute to a greater understanding of maternal and child diet, health and well-being from medieval Scotland, an area of research that is still very much underrepresented. 


Barrett, J H and Richards, M P 2004. ‘Identity, Gender, Religion and Economy: New Isotope and Radiocarbon Evidence for Marine Resource Intensification in Early Historic Orkney, Scotland, UK.’ European Journal of Archaeology 7 (3): 249-271.  

Beaumont, J., Craig Atkins, E., Buckberry, J., Haydock, H., Horne, P., Howcroft, P., Mckenzie, K., and Montgomery, J. (2018). Comparing apples and oranges: Why infant bone collagen may not reflect dietary intake in the same way as dentine collagen. American Journal of Physical Anthropology, DOI: 10.1002/ajpa.23682, 1-17. 

Carver M.O.H., Garner-Lahire, J., and Spall, C.A. (2016), Portmahomack on Tarbat Ness: Changing Ideologies in North-East Scotland, Sixth to Sixteenth Century AD. Society of Antiquaries of Scotland, eBook: 

Carver, M O H and Spall, C A 2004. ‘Excavating a parchmenerie: archaeological correlates of making parchment at the Pictish monastery at Portmahomack, Easter Ross.’ Proceedings of the Society of Antiquaries of Scotland 134: 183-200. 

Curtis-Summers, S, Pearson, J A & Lamb, A L 2020 ‘From Picts to Parish: stable isotope evidence of dietary change at medieval Portmahomack, Scotland’, Journal of Archaeological Science Reports 31: 1–20. 

Czére, O., Fawcett, J., Evans, J., Sayle, K., Müldner, G., Hall, M., Will, B., Mitchell, J., Noble, G., and Britton, K. 2021. Multi-isotope analysis of the human skeletal remains from Blair Atholl, Perth and Kinross, Scotland. Insights into the diet and lifetime mobility of an early medieval individual. Tayside and Fife Archaeological Journal 27: 31-44.  

King, S E 2000. The human remains from Tarbat Old Church, Portmahomack: The Specialist Report. Unpublished report. 

Modzelewski, K. (2008). Dietary Analysis of an Early Historical Southeastern Scottish Population. Unpublished MA Thesis, The University of Reading.

Richards, M.P., Fuller, B.T., and Molleson, T.I. (2006). Stable isotope palaeodietary study of humans and fauna from the multi-period (Iron Age, Viking and Late Medieval) site of Newark Bay, Orkney. Journal of Archaeological Science 33: 122-131.

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