The Vestal Virgins of Rome kept the sacred flame of the city burning, bound to thirty years of chastity in service to Vesta
Rome bound the safety of the entire city, symbolically, to the unbroken chastity of six women serving in a single temple.
According to Plutarch's Life of Numa, the legendary second king of Rome established the order of the Vestals to tend an eternal flame in the Temple of Vesta, goddess of the hearth, believing the city's own security depended on the fire never going out. Girls were selected between roughly six and ten years old and served a fixed thirty-year term, traditionally divided into ten years learning the rites, ten years performing them, and ten years teaching the next generation. Their chastity was not a private virtue but a public office: an unchaste Vestal was thought to endanger Rome itself, which is why the penalty for breaking the vow was so severe. Plutarch treats the whole arrangement as evidence of how seriously early Rome linked ritual purity to civic survival, describing the Vestals' duties alongside Numa's other religious reforms.
Plutarch was writing centuries after Numa's semi-legendary reign, so his account blends historical practice with foundational myth-making about Rome's origins.
Life of Numa