Battle of Carrhae, May 6th, 53 BC

The Senate of Rome planned no war against Parthia, arguing that the Parthians were protected by peace treaties validated by Rome and thus any betrayal of Roman attack would be set up. But relentless or insatiable, Crassus crossed the Euphrates River and offered battle to a Parthian army in the Carrhae region. Cassius, one of the aides, suggested that the infantry enter the battle line, dividing the cavalry by the flanks. The army maneuvered to respond to this device when Crassus contravened: that the legions, with their cohorts, formed a huge square supported by light cavalry and infantry. We understand that Crassus' big mistake was not the choice of battle order but the inconsistency in its execution. If he had adopted Cassius' line, he might have been defeated earlier, for either the cataphracts would have split the army by striking in the center or the archers would have spun around the long line, disrupting it and isolating parts.