Alexander died in Babylon in 323 BC, of unknown causes. Poison, murder, or a fever after a battle have all been suggested. At his death, he was planning a series of campaigns that would have begun with an invasion of Arabia. In the years following his death, a series of civil wars tore his empire apart. Several states were then ruled by the Diadochi, Alexander's surviving generals and heirs. They fought and conquered each other. The largest surviving piece was the Seleucid Empire.