Language is a funny thing and no language is as funny, weird or baffling as English. Perhaps more than any other tongue, English has been influenced by almost every culture and language it has come into contact with. The purpose of this series is to highlight some of the more interesting instances where an event, cultural practice or person has entered the vocabulary of the modern English speaker.
The word decimation is one of those words where the common usage is different to its actual definition. It is technically defined as ‘reducing by one-tenth’ but is now generally used in the sense of ‘reducing by a large or extreme proportion’. For example, sports commentators often state that a team (10 players for the purposes of this example) has been decimated by injury. By this, they may mean that three or four (or more) of the regular players are injured but technically this would mean that only one player is injured, hardly an unusual occurrence in professional sport.
Another example may be that the population of a particular animal is said to have been decimated by hunting. Once again, the intended meaning is far more severe than the actual definition conveys.
As some may deduce from the prefix ‘deci’, Latin for ten (as in decade: ten years and December: the tenth month in the original Roman calendar), the word decimation has its origins in Ancient Rome.
And what an origin it is.
If there is one thing that the Roman army was famous (or infamous) for it was for its discipline. It was one of the key pillars of its centuries-long period of military success.
It is perhaps unsurprising, therefore, that when Roman soldiers failed to meet those lofty standards as a unit, such as by fleeing in battle or engaging in mutiny, they were dealt with in a particularly ruthless manner, known as decimatio.
A traditional Roman legion was organised into 9 cohorts of 480 men and one cohort (the First Cohort) of 960. If a particular cohort was slated for punishment (whether on its own or as part of the legion as a whole), it was divided into 10-man groups. These groups would then draw lots, resulting in one unfortunate individual being singled out.
This is where it gets vicious.
The chosen soldier was then publicly beaten or stoned to death by the other nine members of the group. In effect, the executors were also punished by not just having to execute their comrade but having to do so in a manner that was neither quick, painless or bloodless. Of a cohort of 480, 48 men would be executed in such a manner. To add insult to injury, instead of the usual rations of wheat, the survivors were given barley, which is much harder on the stomach. 
All of this occurred regardless of the guilt, rank or distinction of the individuals involved.
The earliest recorded incidence of decimation occurred in 471 BCE, when Rome was jostling with its neighbours for regional influence.
The practice appears to have fallen out of use by the early 1st Century BCE, but it was famously revived by Marcus Licinius Crassus at the height of the Third Servile War (the famous revolt of Spartacus) in 71 BCE. It is not clear whether Crassus ordered that a single legion be decimated or if it was his entire army, in which case as many as 4,000 men would have been executed by their peers.
Decimation continued to be practised during the Roman Republic and the later Roman Empire, though it was a rare occurrence.
Interestingly, the practice has also been used in the centuries since the fall of the Western Roman Empire. Perhaps the most notorious incidence occurred in the aftermath of the Battle of Breitenfield in 1642 during the Thirty Year’s War when the defeated Imperial Army (of the Holy Roman Empire) was subjected to decimation by its commanders.
Even as later as 1914, a colonial French company was decimated after it refused to attack as ordered.
However, some historians both modern and ancient alike have questioned the effectiveness of decimation as a punishment, arguing that it would have almost inevitably led to a collapse in morale, not to mention the reduction in fighting strength. One modern historian notes that those commanders, both of the Roman Empire and later centuries, who used the practice did so out of an ‘excessive love of ancient practices’ rather than because it was proven to be effective.
So there you have it. Originally, decimation may not be as bad as it is intended nowadays in terms of proportions, but, really, it was just as bad as it is intended nowadays.