Explanation: The Romans Legions had an extensive system of rewards and punishments to motivate soldiers. Soldiers who performed well could receive medals, bonuses, and promotions. Soldiers who performed poorly, on the other hand, could receive docked pay, adjusted rations, beatings, and even execution for serious offenses. What's more, the Romans were not exactly adverse to collective punishment - while a single man would not fuck up an entire legion's fate, camp-groups of 8-10 soldiers could be and often were punished for minor disciplinary infractions by one of their own - a serious incentive to self-police!
Reducing rations, however, also comes with the risk of reducing efficacy - a poorly-fed soldier is a poorly-performing one, after all. What was the Roman solution? Changing a soldier's allotted ration from wheat, to barley! Barley feeds a man fine, but was considered lower-quality and lower-status food, and getting one's rations changed to barley for a period of time was thus a humiliation as well as a material punishment. You're eating the ANIMAL FEED NOW, SOLDIER! Save those tears for someone who cares!