 Seleucus, who had been "Commander-in-Chief of the Companion cavalry" ("hetairoi") and appointed first or court chiliarch (which made him the senior officer in the Royal Army after the regent and commander-in-chief Perdiccas since 323 BC, though he helped to assassinate him later) received Babylonia and, from that point, continued to expand his dominions ruthlessly.Seleucus established himself in Babylon in 312 BC, the year used as the foundation date of the Seleucid Empire.The rise of Seleucus in Babylon threatened the eastern extent of Antigonus I territory in Asia.