The Roman census and legal record — both incompletely preserved but informative where they survive — record households that frequently include a mix of biological relatives, legal dependents, enslaved persons, freed persons, and others. The assumption that a plausible number of adults and children found together in a house must be a biological nuclear family is not supported by what the Roman sources tell us about how households were actually constituted.
This historical context makes the DNA study’s finding — four unrelated individuals found together in the House of the Golden Bracelet — not surprising but expected. A prosperous Roman household found in the act of fleeing or sheltering in 79 CE could easily have included people of several different kinds of relationship: an owner, an enslaved person charged with the care of the owner’s child, a visitor, a client, an employee. Any of these configurations would produce a group of individuals who were not closely biologically related and who nevertheless had strong reasons to be in the same place at the same moment.
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## The Role of Strontium Isotopes
Alongside the ancient DNA analysis, the 2024 study incorporated strontium isotope analysis — a complementary technique that addresses a different question about the individuals’ lives. While DNA speaks to genetic ancestry, strontium isotopes in tooth enamel speak to geographic mobility: specifically, to where an individual spent their childhood, when their teeth were forming.
Strontium occurs in the environment in several isotopic ratios that vary by geology. The rocks, soil, and groundwater of different regions have characteristic strontium isotope signatures, and these signatures enter the food chain and the water supply. Children consuming food and water from a particular region will incorporate the local strontium signature into the enamel of their developing teeth. Because tooth enamel does not remodel after it forms, this signature is permanently recorded. Comparing the strontium ratio in an individual’s tooth enamel against the local geological signature of the site where they were found can indicate whether they grew up locally or migrated from elsewhere.