The twins wanted to build a city but couldn't agree on which hill to build the city on. Romulus wanted one on Palatine hill, and Remus wanted one on Aventine hill. So they built their own cities with walls.
Remus visited Romulus and climbed Romulus' wall making fun of him saying how his walls were so easy to invade. In response Romulus killed is brother due to how annoyed he was about it all.
There is a legend saying Romulus was the first king of Rome in 753BC, he populated his city with runaway slaves and convicted criminals. He stole women from a tribe called Sabine, he wanted to provide wives for the slaves and criminals that populated his city.
The Sabine tribe wasnt too happy about what Romulus was doing, so they declared war against Rome.
The war went on for many years until the Sabines and Romulus reached an agreement and the Sabine became a part of Rome under the kingship of Romulus
The legend then ends with Romulus being carried up to the heavens by his father and was soon then known as the God Quirinus