When a vacancy opened among Rome's six Vestal Virgins, the Pontifex Maximus selected a replacement from a pool of eligible candidates, freeborn girls between roughly six and ten years old, both of whose parents were living, drawn from families of good standing at Rome. Ancient sources describe an original lottery among twenty qualifying candidates, though by the late Republic and Empire it became increasingly common for families to volunteer a daughter directly, sometimes competing for the honor, since a Vestal enjoyed legal and social privileges, including freedom from her father's legal authority and the right to make a will, unavailable to other Roman women.
Once chosen, the girl was formally taken into the priesthood through a ceremony ancient sources call the captio, drawing on the same verb Romans used for the seizure of a prisoner or the capture of enemy territory, language modern historians have read as marking the girl's complete removal from her birth family's legal authority and her transfer into a wholly different, sacred category of person, neither simply a child, a wife, nor a widow, the three categories that otherwise defined a Roman woman's legal identity.