In June 53 BCE, a Parthian force of roughly 10,000 mounted archers and cataphracts under General Surena annihilated seven Roman legions commanded by Marcus Licinius Crassus near Carrhae in Upper Mesopotamia. Approximately 20,000 Roman soldiers were killed and 10,000 captured. Crassus himself was killed during failed negotiations. The defeat halted Roman expansion eastward for generations and established the Euphrates as the boundary between Roman and Parthian spheres. Captured Roman legionary standards became a source of diplomatic contention for decades. The battle demonstrated the effectiveness of Parthian horse archery against heavy infantry.