The Writer’s Guide to Besieging a Castle
Even though castles could be easily avoided by an invading force, it was often a bad idea. Attacks could be launched from them, with the soldiers retreating to their safety. During much of medieval Europe, if you wanted to take territory you had to deal with the castle of its king or lord. This usually involved a siege. Sieges are popular in books, movies, TV shows, and video games since they are full of drama and tension. Examples include the sieges of Winterfell and King’s Landing in “Game of Thrones,” the siege of Adamant in the game Dragon Age: Inquisition and the siege of Silasta in Sam Hawke’s “City of Lies.”
Today I will be covering the tactics used during a siege. Next week’s article will cover siege engines.
As always, magic is the exception to the rules. Because magic.
Since early castles were made of wood, setting fire to them was an effective means of neutralizing them. Unfortunately, we don’t have a lot of documentation of this method. The most prominent example is a section of the Bayeaux Tapestry in which two men with torches are attempting to set fire to Chateau de Dinan.  However, from the artwork of the period, it appears that most timber castles were not bare wood but had a layer of plaster applied to them.
The most direct route of taking a castle was to assault the gates and/or walls. This is where siege engines were used. Some, such as the siege tower, were designed to get soldiers onto the tops of the walls. From there, they could fight down to the gates and open them for the rest of the army. Others, such as battering rams, catapults, and trebuchets were designed to go through a castle’s defenses.
A direct assault was usually the quickest way of taking a castle or for that matter, a fortified city or town.  But it was also the riskiest and the most likely to result in high casualties. Because of the defensive features of castles, a small garrison could hold out for a long time. For example, in 1403, thirty-seven archers defended Caernarfon Castle against two assaults by allies of Owain Glyndŵr. 
Sapping or Mining
Sapping involved tunneling under the walls. People who performed these tasks were known as sappers. Either the miners would tunnel under the walls completely, coming up instead them, or they would collapse the walls. To do that, a void would be dug underneath them, stabilized by props and/or beams. Once complete, the beams would be removed, collapsing the void and the walls above it.  The easiest way to remove the supports was to set a fire in the void. There were some accounts that pigs were also trapped in the void before it was set on fire. It was thought that the pig fat helped the fire to burn hotter and faster.
If the defenders realized a tunnel was being dug, they could dig one of their own and try to intercept the sappers. Sapping was so feared that some castles surrendered as soon as they learned the sappers were at work, such as the castle of Margat in 1285. 
Once gunpowder became available, explosive charges were used to collapse the walls and gates. One example is the Siege of Godesberg in 1583.  A literary example is the battle of Helm’s Deep in “The Two Towers.”
Writer’s Tip: Sappers are rarely used in novels. I would love to see a siege in a book that was ended using sappers.
The safest way to take a castle or fortified city or town, was to cut them off from being resupplied and starve them out. However, this was the most time-consuming method. There are accounts of besieged castles lasting weeks, months, and in a few cases, years, if they were well supplied. Some besieging armies tried to speed up the process by using siege engines to fling corpses over the walls, hoping they would spread disease.
The danger to the besieging force was that they were stuck in one place for an extended length of time, leaving them vulnerable to attack by another enemy force.
Betrayal rarely makes the list of besieging methods, but it ended several sieges during the Middle Ages. A person inside the castle would open the gates to the attackers. They could either be someone who had been convinced to betray the castle or a member of the enemy force that infiltrated it.
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Copyright © 2021 Rebecca Shedd. All rights reserved.
 Allen Brown, Reginald (1976) . Allen Brown's English Castles. Woodbridge, UK: The Boydell Press. ISBN 1-84383-069-8.  Friar, Stephen (2003). The Sutton Companion to Castles. Stroud, UK: Sutton Publishing. ISBN 978-0-7509-3994-2.  Friar, Stephen (2003). The Sutton Companion to Castles. Stroud, UK: Sutton Publishing. ISBN 978-0-7509-3994-2.  (in German) Ernst Weyden. Godesberg, das Siebengebirge, und ihre Umgebung. Bonn: T. Habicht Verlag, 1864, p. 43.  Friar, Stephen (2003). The Sutton Companion to Castles. Stroud, UK: Sutton Publishing. ISBN 978-0-7509-3994-2.  Allen Brown, Reginald (1976) . Allen Brown's English Castles. Woodbridge, UK: The Boydell Press. ISBN 1-84383-069-8.