reregarde

Old French rere came from Latin retro (backward, behind), and garde from Frankish warda (watching, guarding). The reregarde — the rear guard — was the division of an army that marched last and faced backward, responsible for protecting the main force from attack from behind. This was among the most dangerous assignments in medieval warfare: when an army retreated, the rearguard fought while everyone else escaped.

The Battle of Roncevaux Pass in 778 CE was the rearguard action that became legend. Charlemagne's forces were withdrawing from Spain when Basque warriors ambushed his rearguard in the Pyrenees. Roland, commanding the rearguard, refused to summon help until it was too late and was killed with most of his men. The Chanson de Roland, composed centuries later, made the rearguard action the defining moment of medieval military honor.

Wellington's Peninsula Campaign (1808-1814) was largely a series of rearguard actions as British forces withdrew before superior French numbers, then turned and fought when the terrain favored defense. The Light Division under Robert Craufurd became the most celebrated rearguard in British military history — retreating in perfect order, fighting at every defensible point, then withdrawing before being encircled.

Today rearguard action describes any defensive effort to slow an inevitable defeat — political, commercial, or cultural. A government fighting a losing legal battle is fighting a rearguard action; a declining industry delaying technological displacement is fighting a rearguard action. The military meaning has generalized into any skilled, disciplined resistance to an outcome that cannot be stopped.