The arrival in Alexandria of Julius caesar gives Cleopatra her first chance of a wider role in the world. She seizes it, becoming the mistress of the man who is now unmistakably - after his defeat of Pompey - the most powerful Roman. Caesar spends the winter of 48-7 BC in Egypt, helping the young queen suppress the forces of her even younger brother (who fails to survive these events).

Soon after Caesar's departure from Alexandria, Cleopatra gives birth to a son (in the summer of 47), whom she claims - almost certainly correctly - to be Caesar's. In 46 Caesar invites Cleopatra to Rome with her son (subsequently known by the nickname Caesarion, 'little Caesar') and provides them with a villa. After Caesar's assassination, in 44, she returns to Egypt with the child.