Decimation. See the historians (among them Polybius, Book XI), lexicographers, and authors who discuss Roman military discipline.

Decimation was a punishment that the Romans inflicted on soldiers who had collectively abandoned their posts, acted like cowards in battle, or fomented some kind of rebellion in the ranks. In those days, they would assemble the troops, and the military tribune would lead the guilty soldiers before the general, who, after he had sharply reprimanded them for their offenses or crimes in front of the entire army, would put all their names in an urn or a helmet and, according to the nature of the crime, draw from the urn five, ten, fifteen, or twenty of the guilty soldiers’ names. Those the fates selected (the fifth, tenth, fifteenth, or twentieth) would be put to the sword; the rest would be reprieved. This was known as “decimating,” decimare .

To fairly assess the offenses or crimes committed by a group and distribute punishment among them, we must invariably acknowledge that where a group is concerned, it would be a grave mistake to suppose each member of the group is individually guilty of the one crime. When the members of a group are assembled for the affairs of the group, they cannot employ the same prudence, wisdom, and sound judgement that each employs in his individual affairs. The offenses that a group therefore commits are the effect of its being a community, and the influence of a few members who have the authority or skill to persuade the others. The members of a group are angered, motivated, and provoked because they constitute a group, and accordingly they have a certain confidence in their numbers that they would not have were they alone. It follows that the punishments that befall the entire group must be extremely lenient and of a short duration. The truth of this reflection did not escape the Romans, despite the severity of the military discipline they delighted in upholding. That is why Cicero said our forefathers, seeking a prudent compromise, devised the decimation of soldiers who had committed the same offense together, so that all would be afraid, but only a few would be punished ( Oratio pro Cluentio ).