Editing Siege Weapon (section)

===Sappers=== 
A good way to weaken enemy walls was to dig under them, weakening the foundation and making them more prone to fracturing and collapsing. What sappers would usually do is once they were certain that they were directly underneath the enemy’s walls, they’d stash a whole lot of flammable materials and douse it with pig fat (not live pigs, they’re significantly less flammable and more prone to running away) then set everything on fire to collapse the supports and cause a cave-in. It was a dangerous job, but it was effective, so long as the enemy didn’t catch on and start counter-mining. Would-be attackers would oftentimes be literally smoked-out and suffocate if they were discovered. Cave-ins were also rightly feared. 

As modern cities typically have tunnel systems running through them (e.g. for subways, access to water pipes, smuggling), sapping and mining still see some use in urban warfare situations where a heavily fortified building needs to be brought down but anti-aircraft defenses prevent the use of bombers to do so. Moreover, sapping was used extensively by both sides on the western front in WW1, where a team would dig a tunnel until they were underneath the enemy's trenches, and then dig out a cave which was then filled with explosives. The explosions from these dug-out mines were some of the largest non-nuclear explosions mankind ever produced, with some of largest being noticeable as far away as London and Cologne. As a result, extensive countermeasures existed too; you could listen to the walls with a stethoscope or place a bucket of water on the floor of a trench, whose surface would ripple from the microvibrations of the enemy digging underneath. If someone noticed the enemy, a counter-tunnel would be dug underneath and filled with a smaller amount of explosives to bury the enemy in their tunnels. Some of these explosives-filled mines were both never cleared of explosives nor detonated when originally intended, and so remain dangerous to this day; in 1956, one of these mines detonated after it was struck by lightning, and the resulting explosion produced a crater that was 40 meters wide and 20 meters deep (thankfully, the only victims were some cows that belonged to a french farmer).