Undermining, or sapping, is the ancient siege technique used against the walls of a fortification. In the Middle Ages, the strategy was adopted and developed in response to the advent of stone castles in Western Europe.

The advent of castles meant that sieges got longer and longer, and supplies became a more acute problem. Rather than taking a fortification through direct assault, more and more besiegers turned to blockades aimed at starving the inhabitants into submission.

As both castles and cities constituted fortifications that combined military functions with residential spaces, sieges necessarily involved the noncombatant residents, including women and children.

Castles and fortified cities combined military and residential functions. When a besieging army breached a settlement’s defenses, combatants and civilians alike suffered the enemy’s wrath.