Rhea Sylvia was the mythical mother of the twins Romulus and Remus, who founded the city of Rome. According to legend, she was the daughter of Numitor, king of Alba and descendant of Aeneas. Numitor's brother, Amulius, seized the throne and killed Numitor's son. He forced Rhea Sylvia to become a Vestal Virgin, a priestess to the goddess Vesta who is sworn to lifelong celibacy, so that Numitor would not have any heirs.
However, the god Mars took a fancy to Rhea Sylvia and raped her, conceiving the twins. When he learned of this, Amulius ordered Rhea Sylvia buried alive (the standard punishment for Vestal Virgins who did not remain celibate) and ordered the twins set adrift in the river Tiber.