The story about Romulus killing his twin brother, at the moment of the founding of the city is a very old story. It is very very remarkable that in the late Republic, the Romans were fighting civil wars, and of course, it didn't escape their notice that they seemed to be prefigured in the myth with Romulus killing his brother. They actually thought this was a sort of curse on them that they were fated to destroy each other.
Well, the whole Roman psyche was based on violence. If you look at the foundation legends of Romulus and Remus, that's based on fratricide. Right, one brother kills another to found the city. And from that point, it just escalates.
The violence of the early Romans in fact and fiction was born of desperation. In real life, shunned by neighboring tribes, Rome was forced to welcome outcasts, vagrants and fugitives. And they lured their neighbors -- the Sabines , to a ritual of peacemaking.
And they are all a pretty desperate lot, and Rome, the earliest community that is organized in that way of course, is a place where no woman wants to go. So they haven't got any women, that's the first problem.
And so the Romans, Romulus in particular got an idea. New religious festival, let's invite the neighbors, bring your wife and kids, especially the daughters.
The Sabines were wary, but accepted. As the festivities went on into the night, the Sabines relaxed their guard. It was what the Romans were waiting for. Romulus gave the sign, and they attacked. They grabbed the women, and drove off the Sabine men, the ones they didn't kill. When painters of a later age portrayed the rape of the Sabine women, they imagined the classical city. They were wrong. The early Romans were primitive people, struggling desperately to survive. The grim stories of the first Romans were as surprising to Livy as they are to us. They certainly didn't provide the role models he was looking for. His little book turned into one of the most monumental histories ever written. By the time he died in 17 A.D., it had grown to 142 volumes, all written laboriously in wax. It had absorbed his entire life. Livy's chronicle was the best seller of his day. It was more successful than he could ever have hoped, but had no effect, whatsoever, on the moral chaos of the empire. Even 142 books were no match for the influence of so much power. By now, Rome was a Juggernaut, whose momentum was unstoppable. Its course set by its mythic beginnings, whether fact or fiction.