In Roman culture, Vestal Virgins were priestesses vowed to forever remain virginal.
The Doctor was once a Vestal Virgin, second-class, before his travels with Nardole and Bill Potts. According to the Twelfth Doctor, "it's a long story". (TV: The Eaters of Light)
According to her mother Metella, if Evelina had been living in Rome, she could have been a Vestal Virgin. (TV: The Fires of Pompeii)
The City's ziggurat had a tapestry depicting a sentient dinosaur sawing the heads off of Vestal Virgins. (PROSE: Alien Bodies)
Sam Jones referred to an alternate version of herself as "the Vestal Virgin type", and was surprised that Fitz Kreiner would go for that kind of personality. (PROSE: Unnatural History)