Who is Vestal Virgins from The Twelve Caesars and what is their importance?

Generally there are six Vestal Virgins at a time and they serve the goddess Vesta in a temple beside the Forum. They serve for thirty years and have to remain virgins. They are given many privileges and the Chief Vestal Virgin is a highly revered person. One of the Vestal Virgins, Rubria, is raped by Nero.