decimation was death by utter humiliation. soldiers that deserted or disobeyed an order then they would be decimated. The decimation was carried out by fellow soldiers. so you would be tied to a post and clubbed to death by men who you had fought together with, eaten together etc. but decimation could be different, general Scipio after he had defeated Hannibal caught the few soldiers that had deserted, tied them to the road and rode his elephants over them. so decimation was the ultimate humiliation to a soldier.