According to Plutarch, there are many versions of Rhea Silvia's story, and it is not clear which one is real. But this is one of the best known and most widely accepted: When Numitor's brother Amulius became king by force, he made Rhea Silvia become a Vestal Virgin, so she would not have children who could be kings instead of him. But the god Mars seduced Rhea Silvia and she had the twins Romulus and Remus. For Vestals, the punishment for having sex was death. So when people found out she was pregnant, Rhea Silvia was buried alive, which was the punishment for a Vestal Virgin who did not remain a virgin. Her sons were thrown into the Tiber by a servant, but were saved by the river god Tiberinus, who also saved Rhea Silvia and later married her.