Barrier troops

Barrier troops, blocking units, or anti-retreat forces are formations of soldiers that in some armies are placed behind regular troops on a battle line to prevent panic or unauthorized withdrawal or retreat. Barrier troops are used to prevent unauthorized withdrawal of soldiers from the battlefield by any means, including indiscriminate killing. As troops guarding other units are obviously not available to fight the enemy they are a costly, often desperate, measure.

Early history

The concept of barrier troops dates from the earliest days of land warfare, when more experienced troops were regularly placed behind raw recruits to prevent panic and to provide a reserve if needed to stop an enemy advance. Roman legions were regularly backstopped by experienced triarii legionaries of many years' service.

During the Napoleonic Wars, the losses due to troops deserting battle were regularly greater than the losses resulting from combat. Since desertion was relatively easy in that era, the use of barrier troops enabled commanders to retain cohesive fighting units during the course of a long campaign.