It is only through a multidisciplinary approach that we can understand past communities. In the case of the Early Medieval period, documental sources in the Iberian Peninsula are scarce and insufficient to understand the everyday life of the communities. Therefore, bioanthropological studies and the application of new methods – such as stable isotopes analysis (for diet and mobility inferences) and genetics, linked with the archaeological sciences and historical data interpretations, have become a crucial source for the knowledge of past societies.

Fig 1. King Reccared and Bishops, 589 A.D. (in Codex Vigilanus, fol. 145, Library of the El Escorial Monastery)

The paleobiological study of early medieval populations that lived between the rivers of Tua/Tuela and Douro, in the region of Trás-os-Montes, Northeast of Portugal, aims to understand not only how these communities organized their funerary space, how they built graves and conducted funerary rituals, but also their lifestyle, the biological profile of each exhumed individual, pathologies, occupational patterns, diet and mobility throughout their life. In addition to life and death in these communities, the issue of social distinctions within the community and between communities will also be addressed.

All these cemeteries were originated in the Early Medieval period (5th-9th centuries) and reused throughout the Middle Ages (until the 14th century). The sample has a total of 317 individuals.

Fig. 2: Localization of five Early Medieval cemeteries under study in Bragança district (Trás-os-Montes region): Torre Velha (Castro de Avelãs), Laranjal, Quinta de Crestelos (East and West) and Mós (Torre de Moncorvo).

Stable isotopes and mobility

Since the beginning of the 20th century, the early medieval period has been seen as a time of migration during which exogenous populations, known as Germans or barbarians, would have arrived in the Iberian Peninsula. To understand the demographics and socio-economic dynamics of this period, it is essential to consider what proportion of the population moved. Sometimes, it’s difficult to observe these migrations trails in the archaeological context. So, when human remains are present, we can use chemistry to trace possible migrations. Strontium stable isotopes (87Sr/86Sr) are the most used tool in studies of mobility in past populations.

First, what are stable isotopes? Stable isotopes are non-radioactive forms of atoms and dozens of elements in the periodic table have them. Radioactive isotopes decay over time (important for dating archaeological finds through ¹⁴C), but stable isotopes don´t decay, staying the same over time. They are present everywhere we live in. Their unique properties can be used in a variety of studies. In archaeology, they can be used for access information about mobility and diet in human remains. How does this information get recorded and how can we read them?

Strontium stable isotopes (87Sr/86Sr) are measured in bones and teeth, functioning as markers of the geology of the areas where individuals grew up and where they died. The strontium (Sr) is absorbed through food and incorporated into bones and teeth. As Sr is predominantly deposited in skeletal tissues, enamel and dentin of teeth should be the most used for the analysis. To define the values of the local Sr, local fauna and a sample of bone from each individual will be analysed, which allows an isotopic signature of the area. The bone remodels throughout life, absorbing the Sr levels of the places where a person lived. These values make it possible to compare the local Sr, the Sr of the human bone and the levels of Sr retained in the tooth enamel. If the Sr levels are different, these individuals will be considered “non-local”. To Sr isotopes analysis should be added oxygen stable isotopes (δ¹⁸O), offering information about water resources available at the place of birth.

Strontium stable isotopes analyses applied in other areas of the Iberian Peninsula have shown that migration would have been limited. Will we have the same results in the NE of Trás-os-Montes? This is the question that we intend to answer during this project.

Fig. 3: Burial from the 11th century (Torre Velha, Castro de Avelãs).

Stable isotopes and diet

We can also use stable isotopes analysis to access diet information. Paleodiet studies not only allow us to make inferences about the type of food consumed in a region at a given time but also provide very important data on population mobility, helping to identify non-locals.

We can analyse diet through carbon stable isotopes (δ¹³C) and nitrogen (δ¹⁵N) of bone collagen, indicative of the consumption of different types of plants, as well the food origin – marine and terrestrial. The carbon stable isotopes (δ¹³C) are useful to identify the type of vegetable resources consumed, based on the mechanisms of two photosynthetic groups of plants: C3 and C4. Most plants in environments considered to be temperate belong to the C3 group (wheat, rice, vegetables, etc.), while the C4 group is composed mainly of grass considered tropical, such as millet, sugar cane and sorghum. Nitrogen stable isotopes (δ¹⁵N) are used to distinguish between a diet rich in meat and a diet rich in plants, and can also distinguish the consumption of marine or freshwater resources.

To define the isotopic ratio of carbon and nitrogen, the compact bone is preferably analysed. If possible, it is important to add a tooth to the bone sample because, while the bone reflects the individual’s diet over the previous 10 to 30 years, the dentin preserves diet signs during childhood. Important differences in the values of bone and dentin isotopes may be found, which indicate a change of location. As for mobility, to determine the isotopic signature of potential food resources consumed by the population, it is also necessary to determine the values of local faunal remains.

As an example, in the archaeological site of Torre Velha in Castro de Avelãs (Bragança), we could observe that the first individuals analysed (n=7) had a diet rich in terrestrial proteins from animal origin, but some individuals showed a slightly higher consumption. Could it mean social differentiation? Furthermore, the values of δ¹³C do not indicate the consumption of C4 plants. More findings of this issue will be published soon.

The proposed multidisciplinary approach can answer several pertinent questions about these communities, concerning life habits, diet, social distinctions, and many others. The final aim is to characterize the daily lives of these communities and attempt to integrate them into the political and religious reality of their time, producing a historical synthesis.

Sofia Tereso is an Archaeologist, specialized in Biological Anthropology since 2009 (master’s degree, DCV- Faculty of Sciences and Technology, University of Coimbra). Since then, she has participated in several research projects within the two areas of study. She is currently a Ph.D. student in Biological Anthropology at the University of Coimbra and a research member of CIAS|UC – Research Centre for Anthropology and Health and IEM|NOVA-FCSH – Institute for Medieval Studies.