The Vestal was not merely a mode of representation. She was also a symbol that could be manipulated. Archaic Roman religion was based on and steeped in magical practice. By “magical practice” I mean that technology of analogy as defined by Tambiah: “Magical acts … constitute ‘performative’ acts by which a property is imperatively transferred to a recipient object or person on an analogical basis.” Magic, since Frazer, has traditionally been divided between the imitative and the contagious. In imitative magic, the law of similarity applies: “like produces like”; in contagious magic, the law of contiguity applies: “objects which have been in contact, but since ceased to be so, continue to act on each other at a distance” (Frazer 1991, 1: 52). The Vestal, who preserved the inviolability of Rome by preserving the inviolability of her body, exemplifies both forms of magic and indeed shows their overlap and a certain arbitrariness in the distinction. Imitative magic is perhaps better characterized as metaphoric (similia similibus): as she remained integra, so did the city. The Vestal’s body served as the microcosm of the city.
Again, this is abundantly clear from the ancient sources. The Vestal must be not merely a virgin but physically perfect in every respect. The potential candidate was examined by the Pontifex Maximus to guarantee this. Both parents must be living, and neither she nor her father emancipated, since this would make her technically an orphan and hence imperfect. Her parents’ marriage must have been perfect. Neither of them could be divorced or ex-slaves or found to have engaged in negotia sordida. Should she fall sick, she must be removed from the aedes Vestae and cared for outside the holy area by a married woman (Pliny 7.19.1). Most importantly, as we have noted, her life and powers were circumscribed by the walls of the city.
Holt N. Parker, “Why Were the Vestals Virgins? Or the Chastity of Women and the Safety of the Roman State” (2004)