Rhea Silvia
According to Livy's account of the legend, she was the daughter of Numitor, king of Alba Longa, and descended from Aeneas. Numitor's younger brother Amulius seized the throne and killed Numitor's son, then forced Rhea Silvia to become a Vestal Virgin, a priestess of the goddess Vesta. As Vestal Virgins were sworn to celibacy, this would ensure the line of Numitor had no heirs. Rhea, however, became pregnant with the twins Romulus and Remus by the god Mars.