Sapping

By using the sap, the besiegers could move closer to the walls of a fortress, without exposing the sappers to direct fire from the defending force.

Once the saps were close enough, siege engines or cannon could be moved through the trenches to get closer to—and enable firing at—the fortification.

Prior to the invention of large pieces of siege artillery, miners could start to tunnel from the head of a sap to undermine the walls.

A way to force entry into a fortified structure was to dig a mine or sap under defensive walls, typically shored up by wooden props.

To breach the walls, Ferdinand ordered his soldiers to dig into the feldspar supporting the side of the mountain and place an explosive charge.

After completing a mine it was filled with explosives, sometimes hundreds of tons, and detonated, followed by an attack on the surprised survivors from the destroyed position.

Russian saps were widely used in the First World War, for example during the Battle of the Somme, when four of them were further equipped with Livens Large Gallery Flame Projectors.

Similar tactics were used in the Korean War by the Chinese People's Volunteer Army, when they dug under the Yalu River to attack US troops, and by Hamas, when carrying out tunnel warfare from the Gaza Strip against Israel.