3. Pigs
Yes, pigs, honestly. I wanted to include some sort of giant, city crushing siege engine and considered the Helepolis, which was a nine storey high siege tower, with its own battery of catapults. Whilst it was a fantastic feat of engineering, it just wasn't that inventive. So I've gone for something much more subtle and possibly, in its own way, more destructive. Yes, the humble swine was used as a weapon, apparently to great effect, for in the siege of Rochester Castle in 1215 a barrage of catapult fire that was kept up day and night failed to break the walls or the keep open. But where they failed pigs succeeded. In an army the sappers are combat engineers. It is their job to carry out siege operations such as dig trenches or fortifications, build or destroy bridges and generally carry out any warfare engineering required. One of their chief roles was the undermining of fortifications. Because the catapults couldn't breach the walls of Rochester castle King John ordered picks to be made day and night so that a mine could be built beneath the walls. The plan was successful and the attackers made it inside the wall but the defenders had retreated to the keep. John ordered another mine to be built beneath the keep, but this time he sent for "forty of the fattest pigs of the sort least good for eating". Once the sappers had completed the mine the pigs were driven into it and a fire was started. Pig fat is very rich and it burns hot. Between the heat of the great fire and the collapsing of the tunnel, the keep was cracked open. This didn't quite mark the end of the siege but it wasn't long after that that it came to a conclusion. As a result, the siege of Rochester marked a drop in confidence in castles as the Barnwell chronicler wrote, "Our age has not known a siege so hard pressed nor so strongly resisted ... Afterwards few cared to put their trust in castles". You may do well to remember that whilst pigs are delicious, they are also a powerful siege weapon.