The city of Rome has a legendary origin story involving twin brothers, Remus and Romulus. Various versions of this story exist, and the details differ sometimes significantly; however, the stories share some basic details and all the same way, with the triumph of one brother over another and the founding of the City of Rome.

As the story goes, a woman named Rhea was married to Mars, the god of war. They had twin sons, Remus and Romulus. In order to prevent her children from being killed by other gods, Rhea hid her sons in a basket and sent it floating down the River Tiber. Finding the basket was not a person but a female wolf named Lupa, who reared the boys as her own. She gave them her own milk, and a woodpecker gathered food for them.

The boys grew up a bit, and the wolf nudged the boys to a spot where they would be found by people. A shepherd, Faustulus, and his wife, Acca Larentia, discovered Remus and Romulus and treated them as their own children.

As adults, the twins decided to build a city at the point where their wolf "mother" had found them. They also decided that the city that they would build should have a king–one king. They chose to have a contest, with the winner being crowned king. When it appeared that Remus would win, Romulus set upon his twin brother and killed him. He then founded the city, named it after himself, and declared himself king. The date given for this last set of events is 753 B.C., and some sources even list a day: April 21.

Another version of the story has the twins quarreling over where to found the city, with Remus preferring the Aventine Hill and Romulus wanting to build on the Palatine Hill, and that the brothers used augury, an ancient kind of fortune-telling, in order to choose.

Yet another version has Romulus building a wall and his brother making fun of the wall, even jumping over it to illustrate how little it could keep enemies out. This then was the genesis of Romulus's fratricidal rage.

In terms of the paternity of the boys, some stories say that their father was the great Greek hero Hercules and other stories say that they were descendants of Aeneas, the Trojan prince who is said to have come to the area after the Trojan War.

Another version of the story has their mother being Rhea Silvia, the daughter of Numitor, the king of Alba Longa. Amulius killed all of the male heirs of Numitor, his brother, and took his place on the throne. When Remus and Romulus came of age, they got revenge on Amulius, killing him, and restored their grandfather to the throne.