The isotope analysis of the Puig Castellar and Ullastret sites suggests distinct mobility patterns among these individuals, who would not have been randomly selected.
The practice of the nailed heads ritual varied among Iberian communities in the northeast of the Iberian Peninsula, rather than representing a uniform symbolic expression. In some settlements, the display of external individuals served as a symbol of power and intimidation, while others may have prioritized the veneration of their own community members.
This conclusion comes from a study led by the Universitat Autònoma de Barcelona (UAB), which analyzed the mobility patterns of Iron Age human communities from the last millennium BCE. Researchers examined seven skulls with embedded nails, belonging to men from two archaeological sites: the ancient city of Ullastret (located in present-day Girona) and the settlement of Puig Castellar (Santa Coloma de Gramenet, Barcelona).
The study, published in the Journal of Archaeological Science: Reports, was coordinated by researchers from the UAB’s Department of Animal Biology, Plant Biology, and Ecology. It also involved collaboration with scholars from the Museum of Archaeology of Catalonia (MAC), the Museum Torre Balldovina, and the universities of Lleida, Bordeaux (France), and Tübingen (Germany).
Severed heads: more than just simple war trophies
Severed heads were a unique funerary practice within the Iberian world and represent an exceptional opportunity to analyze these communities, of which very little archaeological record exists since cremation was the predominant burial ritual. This practice consisted of the public exhibition of the skulls of certain individuals, subjected to a post-mortem treatment. Some of these skulls have been recovered with signs of nailing and in some cases with an iron nail still in place.
“Who were these individuals and for what were their heads used?” Traditionally, archaeologists have debated whether the skulls were war trophies — to intimidate their enemies — or venerated relics of important community members. These hypotheses, however, based on oral and ethnographic sources, have not yet been verified, nor has there been in-depth studies on the relationship between these groups and the land they inhabited. “Our premise in approaching the study was that if they were war trophies they would not come from the sites analyzed, while if they were venerated individuals, these would most likely be local,” explains Rubén de la Fuente-Seoane, an archaeologist at the UAB and first author of the study.
“Our results reveal that the individuals from Puig Castellar and Ullastret would not have been randomly selected. There would have been a homogeneous trend towards men in these rituals. However, the mobility and localization patterns suggest a greater diversity, which could also imply social and cultural differences among the individuals of the two communities,” says the UAB researcher.
Isotope analysis reveals differences between the sites
To carry out the study, the research team combined bioarchaeology and the analysis of stable strontium and oxygen isotopes in the dental enamel of seven severed skulls of men recovered from Puig Castellar and Ullastret, together with archaeozoological data and a detailed sampling of sediment and vegetation collected in the vicinity of the sites.
The results of the strontium isotopes of the sediment and vegetation allowed researchers to define the reference range of the strontium in the area near each site (bioavailable strontium). This in turn made it possible to discern which individuals coincided or not with this range and, therefore, identify whether they were local or not.
“At Puig Castellar, the isotope values of three of the four individuals differ significantly from the local strontium reference, which suggests that they were probably not from the local community. In contrast, Ullastret revealed a mixture of local and non-local origins. This result suggests that the practice of severed heads was applied in a different way at each site, which seems to rule out a homogeneous symbolic expression. But more research is needed to be sure,” says de la Fuente-Seoane.
The fact that in Puig Castellar the skulls were exposed in an area such as the wall makes the researchers opt for the hypothesis that the reason for their exposure was aimed at the demonstration of power and coercion, both for internal repression and towards a group outside the community.
In the case of Ullastret, the two local individuals were found in a street, in the middle of the city, which suggests that they were exhibited on a wall or doorway of the adjacent houses. This fact would provide support to the hypothesis suggesting that they could have belonged to important people of this community, venerated or vindicated by its inhabitants. A third Ullastret skull, of possible foreign origin, was found in one of the external walls of the settlement, which could represent a war trophy.
New tools to help understand the Iberian society
The results of the study reveal for the first time direct evidence of human mobility patterns during the Iron Age in the northeastern Iberian Peninsula, and provide new perspectives on the territorialisation contexts of northeastern Iberia.
Previous research on Iberian territorial management suggested differences in how these societies exploited the resources surrounding them.
With this study researchers were able to see that the skulls found at Puig Castellar and Ullastret also show different mobility patterns, given that the values of the humans and their relationship with the values of the area are completely different in each site. The faunal samples also reveal a very differentiated resource management, in coherence with the typology of each of the settlements.
“This differentiation reflects a dynamic and complex society with important local and external interactions. Our study is a first approach to this archaeological problem using a method that is revolutionizing the way we study mobility in the past. At the same time, it suggests that the selection of individuals for the severed heads ritual was more complex than initially thought,” indicates Rubén de la Fuente-Seoane.
The study underlines the importance of integrating bioarchaeological and isotope data to improve the understanding of social structures and human interactions in the past.
“We have established a local strontium reference based on a rigorous protocol, applying in humans a pioneering methodology in Catalonia that, moreover, serves as a first step towards the creation of a Catalan map of bioavailable strontium. This will favor other future studies and the group of archaeologists studying mobility,” concludes the UAB researcher.
Reference: “Territorialisation and human mobility during the Iron Age in NE Iberia: An approach through Isotope Analyses of the Severed Heads from Puig Castellar (Barcelona, Spain) and Ullastret (Girona, Spain)” by Rubén de la Fuente-Seoane, Diego López-Onaindia, Ferran Codina Falgas, Gabriel De Prado, Conxita Ferrer Álvarez, M. Carme Rovira Hortalà, Marta Díaz-Zorita Bonilla, Ariadna Nieto-Espinet and M. Eulàlia Subirà, 13 February 2025, Journal of Archaeological Science: Reports.
DOI: 10.1016/j.jasrep.2025.105035
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