Rhea was married to Mars, the Roman god of war. Rhea had twin sons. She loved her boys, but there were plots afoot by other gods and goddesses to harm her father, herself, her husband, and her children. To protect the boys, she set them adrift on the river, hoping someone would find them. Who would not love such beautiful boys?
Sure enough, first they were found by a she-wolf who fed them. Then a shepherd and his wife adopted the boys.
As the twins grew older, they decided they did not want to take care of sheep. They wanted to be kings. They decided to build a city on the shores of the Tiber. They both wanted to be the only king. They quarrelled. In a fit of rage, Romulus picked up a rock, killed his brother, and made himself king.
That's how Rome started.