Wikipedia
In the military of ancient Rome, fustuarium ( Greek ξυλοκοπία, xylokopia) or fustuarium supplicium ("the punishment of cudgeling") was a severe form of military discipline in which a soldier was cudgeled to death.
It is described by the Greek historian Polybius in a passage observing that Roman soldiers were motivated to stand fast and maintain their posts by the fear of harsh punishments such as public disgrace, flogging, and death. As a form of discipline imposed on a soldier, fustuarium thus reflected Roman doubts that courage alone was sufficient to ensure the steadfastness of the average soldier — an awareness that Julius Caesar shows in his war commentaries.
Fustuarium was the penalty when a sentry deserted his post and for stealing from one's fellow soldiers in camp. A soldier who committed an act of theft (furtum) against civilians by contrast had his right hand cut off. The fustuarium was also the punishment for falsifying evidence and lying under oath, or for committing the same offence three times.
It is sometimes thought that homosexuality incurred this punishment, but Polybius limits potential offenders to "young men who have abused their persons", that is, who have willingly submitted to penetration. A Roman man could engage in same-sexual relations without loss to his status or perceived masculinity, as long as he took the dominant or penetrative role, but making sexual use of a fellow citizen's body was a violation of the principle of liberty. Acceptable male partners had to be of lower status, in the military typically slaves. A soldier who chose to be penetrated "abused his person" by violating the sexual hierarchy, especially since Romans equated sexual and military dominance. He undermined military discipline if he offered himself as sexually receptive in exchange for gifts or favors. Conversely, when Roman historians condemn incidents of sexual harassment from superior officers, it is emphasized that the subordinate did nothing to encourage the advances. All the behaviors punishable by the fustuarium—desertion, stealing, false witness, sexual misconduct and repeat offenses—thus violate trust ( fides) among fellow soldiers, and the cudgeling was administered communally.
Fustuarium was inflicted on a single soldier who committed an offense, and thereby differs from decimation, when a unit that had mutinied or disgraced itself by cowardice was compelled to select every tenth man and stone or club him to death by their own hands. The distinction between fustuarium and decimation, however, may be illusory and is difficult to discern in passing references by literary sources.
Fustuarium is a strikingly archaic form of punishment at odds with Roman legal practice in the historical era; stoning was also alien to the Romans, except in a military setting, perhaps suggesting the conservatism of martial tradition. Fustuarium may have originated as a religious rite of purification by means of which the unit purged itself through something like a scapegoat or pharmakos ritual. Germanicus, for instance, permitted mutinous soldiers to butcher their leaders to clear themselves of their guilt.
Fustuarium in combination with decimation is relatively rare in the historical record. Incidents include Marcus Crassus, punishing forces defeated by Spartacus early in his command of the war; Apronius, deserters against Tacfarinas; and four occasions during the civil wars between 49 and 34 BC.