In ancient Rome, the Vestals or Vestal Virgins were priestesses of Vesta, goddess of the hearth. The College of the Vestals and its well-being were regarded as fundamental to the continuance and security of Rome. They cultivated the sacred fire that was not allowed to go out. The Vestals were freed of the usual social obligations to marry and bear children and took a 30-year vow of chastity in order to devote themselves to the study and correct observance of state rituals that were forbidden to the colleges of male priests.
“AS far back as it is possible to trace the old religions of mankind, and in cases where primitive religions are still to be observed in savage countries, one finds as a feature of many cults, in various ages and countries, establishments of Virgin Priestesses, or religious votaries as an important adjunct to the worship of the Deity.
“Of these establishments, perhaps the best known is that of the Vestal Virgins of Rome.
“As I know of no exhaustive account of the Vestals in the English language, I have sought in these pages to trace the history of the foundation from its beginning (715 B.C.) to its extinction under Theodosius in a.D. 394, to set forth the status, functions and privileges of its members during this period of over one thousand years; to describe and discuss the temples served and hostels occupied by the Vestals, both as recorded in Latin and Greek authors and as shown by their existing remains; and finally, to give some account of similar foundations in other countries and other ages.”—T. Cato Worsfold
What the intro above says is true; this really is the best book ever written about the Vestal Virgins. I've done tons of research on them, and this book surpasses everything else I've read. It is complete, thorough, and fascinating.
I also highly recommend Robin Wildfang's book, Rome's Vestal Virgins.
Covers a broad range of topics whilst staying concise and (relatively) jargon-free. A solid introductory read into the history of the Vestals.
EDIT
My knowledge definitely needed to be backed up with modern articles because this book was published in 1932 and there has been so much work done on Roman religion since then (particularly about women).
This certainly is a comprehensive work! It was published in the 1930s and some of the information/interpretation is a bit dated. However, there is no arguing with Worsfold's scholarship. I highly recommend this book to anybody interested in the Roman State Religion or in Vestals in particular.