Taylor, Michael j. (2022) “Decimatio: Myth, Discipline, and Death in the Roman Republic.” Antichthon, pp. 1–16 doi:10.1017/ann.2022.9
Around 150 BCE, Polybius wrote that Roman military law contained the fearsome punishment of decimatio:
If the same thing (i.e., acts of cowardice) ever happens to large bodies, and if entire maniples desert their posts when exceedingly hard pressed, the officers refrain from inflicting the fustuarium or the death penalty on all, but find a solution of the difficulty which is both salutary and terror-striking. The tribune assembles the legion, and brings up those guilty of leaving the ranks, reproaches them sharply, and finally chooses by lots sometimes five, sometimes eight, sometimes twenty of the offenders, so adjusting the number thus chosen that they form as near as possible the tenth part of those guilty of cowardice. Those on whom the lot falls are clubbed mercilessly in the manner above described; the rest receive rations of barley instead of wheat and are ordered to encamp outside the camp on an unprotected spot. As therefore the danger and dread of drawing the fatal lot affects all equally, as it is uncertain on whom it will fall; and as the public disgrace of receiving barley rations falls on all alike, this practice is that best calculated both to inspire fear and to correct the mischief.
But historian Michael Taylor noticed that the Romans had only two or three examples of this punishment being carried out before the time of Crassus and Pompey, both of which belonged to the misty times before 300 BCE.
Ancient authors enjoyed recounting extreme and exemplary tales and were drawn to violent and dramatic events. The marked absence of attested decimations in the sources during the Middle Republic is therefore notable given that for the period from 218–167 BC we are remarkably well informed about military affairs. With the notable exception of Caesar’s self-documented campaigns from 58–48 BC, this is probably the best attested period for the entirety of Roman military history from the monarchy to the Late Empire. … for all of this rich sourcing, we do not know of one datable instance of decimatio between Fabius Rullianus (probably 315 BC) and Crassus (72 BC). … And yet, as discussed below, we know of many various lesser punishments meted out to centuries, maniples and cohorts for failure in battle, but never decimatio.
And so Taylor suggests another way of thinking about this punishment:
Rather than being a practical, routine punishment, decimatio seems to have been a civic myth during most of the Republic. As a myth, it served a social purpose, in constructing the authority of the aristocracy while illustrating the importance of battlefield courage and group solidarity. But prior to Crassus, it remained a myth.
He suggests that decimatio was part of the delicate balancing act by which aristocrats tried to keep their privileges while depending on the votes and military service of male citizens. If soldiers believed that their commanders could order a tenth of them executed, they would be more likely to accept whatever milder punishments most commanders actually inflicted. Having a legendary punishment which nobody actually used put aristocrats in a stronger bargaining position.
You can get a copy of this article by contacting the author https://albany.academia.edu/MTaylor