What story does Cassius tell Brutus?

He tells Brutus a story in which he and Caesar were holding a swimming contest across the Tiber river, and Caesar started to drown. Cassius claims that he rescued Caesar and carried him to the shore. He then complains that Caesar has become so powerful that even though he once saved Caesar's life, he must now bow before him.

Cassius then tells Brutus that "Brutus" is just as good a name as "Caesar", and that both names could just as easily rule Rome. He invokes the image of Brutus' ancestor who founded the Roman Republic and expelled the former kings. Brutus, afraid that Caesar will become a king, struggles to decide whether to join Cassius in taking action against Caesar, but ultimately decides against it.