Mining (military) - Middle Ages

Middle Ages

In warfare during the Middle Ages, a "mine" was a tunnel dug to bring down castles and other fortifications. The technique was used when the fortification was not built on solid rock, and was developed as a response to stone built castles that could not be burned like earlier-style wooden forts. A tunnel would be excavated under the outer defenses either to provide access into the fortification or to collapse the walls. These tunnels would normally be supported by temporary wooden props as the digging progressed. Once the excavation was complete, the wall or tower being undermined would be collapsed by filling the excavation with combustible material that, when lit, would burn away the props leaving the structure above unsupported and thus liable to collapse. Later, explosives like gunpowder were used for even greater effect.

A tactic related to mining is sapping the wall, where engineers would dig at the base of a wall with crowbars and picks. Peter of les Vaux-de-Cernay recounts how at the battle of Carcassonne, during the Albigensian Crusade, "after the top of the wall had been somewhat weakened by bombardment from petraries, our engineers succeeded with great difficulty in bringing a four-wheeled wagon, covered in oxhides, close to the wall, from which they set to work to sap the wall"

As in the siege of Carcassonne, defenders worked to prevent sapping by dumping anything they had down on attackers who tried to dig under the wall. Successful sapping usually ended the battle since either the defenders would no longer be able to defend and surrender, or the attackers would simply charge in and engage the defenders in close combat.

There were several methods to resist undermining. Often the siting of a castle could be such as to make mining difficult. The walls of a castle could be constructed either on solid rock or on sandy or water logged land, making it difficult to dig mines. A very deep ditch or moat could be constructed in front of the walls, as was done at Pembroke Castle, or even artificial lakes, as was done at Kenilworth Castle. This makes it more difficult to dig a mine, and even if a breach is made, the ditch or moat makes exploiting the breach difficult. The defenders could also dig counter mines. From these they could then dig into the attackers' tunnels and sortie into them to either kill the miners or to set fire to the pit-props to collapse the attackers' tunnel. Alternatively they could under mine the attackers' tunnels and create a camouflet to collapse the attackers' tunnels. Finally if the walls were breached, they could either place obstacles in the breach, for example a cheval de frise to hinder a forlorn hope, or construct a coupure. The great concentric ringed fortresses, like Beaumaris Castle on Anglesey, were designed so that the inner walls were ready-built coupures: if an attacker succeeded in breaching the outer walls, he would be in a killing field between the lower outer walls and the higher inner walls.