When Numitor's brother Amulius became king by force, he made Rhea Silvia a Vestal Virgin, so she would not have children who could be kings instead of him. But the god Mars seduced her and she had the twins Romulus and Remus. Because of that she was buried alive (put in the earth so she died because she could not breathe), which was the common punishment for a Vestal Virgin who did not remain a virgin. Her sons were thrown into the Tiber by the servant, but were saved by the river god Tiberinus, who also saved Rhea Silvia and married her.
Tiberinus, whence the name of the river Tiber comes, married Rhea Silvia while the twins, Romulus and Remus, were raised by a she-wolf. A few months later a shepherd found them and raised them. When they where a bit older they decided to name a city after its ruler, the only problem is they both wanted to rule. So in the end they decided to fight and Romulus won, while his brother died, and named the city Rome.