Müldner’s team analyzed the bones for chemical clues called isotopes, which are different versions of particular elements.
Based on the geology and climate of where a person grew up, their bones hold telltale traces of isotopes absorbed from the local food and water.
Oxygen and strontium isotopes in the bones of the headless Romans indicate that just 5 of the 18 individuals tested came from the York area, the team reports in the new study, published in the current issue of the Journal of Archaeological Science.
The rest of the men came from elsewhere in England or mainland Europe, possibly from France, Germany, the Balkans, or the Mediterranean.
Traces of carbon and nitrogen show that five of the headless Romans ate very different foods from York’s local population.
And two individuals had a carbon signature from a group of food plants—including sorghum, sugarcane, and maize—not known to have been cultivated in England at that time.
“We haven’t seen such a signature anywhere in Britain before” in the archaeological record, Müldner said.