Hadrian

Jerry Yang to Yahooers: One in Ten of You Is Gone

The Romans used to use to refer to this process of right-sizing 10% of their force as "decimation":

A group selected for punishment by decimation was divided into groups of ten; each group cast lots, and the soldier on whom the lot fell was executed by his nine comrades, often by stoning or clubbing. The remaining soldiers were given rations of barley instead of wheat and forced to sleep outside of the Roman encampment.