This required the use of specialized equipment, techniques, and tactics.
One of the basic tactics of siege warfare was to block the supply of food and water to a castle. This forced the castle and its inhabitants to survive on whatever provisions they had.
If the castle was not prepared for the siege, its inhabitants soon ran out of provisions and had to capitulate. Well-prepared castles could last months or even years in spite of a siege.
The besieging army also had to look out for relieving parties. These were armies sent to relieve the siege and force their way to the castle to bring fresh provisions. The castle’s garrison could also launch an attack at the same time to harass a besieging army on both sides.
Artillery was used to batter the walls of a castle or throw missiles beyond the walls. During the early medieval period, large catapults and trebuchets were used to launch boulders. These boulders would pound the castle walls. Upon repeated attacks, the walls would break down allowing the besieging army to launch an attack.
In the 14th century, cannons and guns became a part of European warfare. Cannons and Guns provided a more potent alternative to traditional catapults in that they could be concentrated on a single point of a castle to bring down the walls. As the guns evolved and grew more powerful, the importance of the castles waned.
Siege towers allowed the attackers to scale the castle walls and get close to the defenders for hand-to-hand combat. These towers were typically made of wood and dragged on wheels close to the castle walls.
The front was protected from arrows and other missiles shot by the defenders on the wall. Once a tower grew close enough to the wall, its front would open and become a sort of bridge on which the attackers could climb and reach the wall.
The defenders used tactics such as fire arrows to sabotage a siege tower. The attackers could counter it by using water-soaked covering to shield the tower.
Battering rams were large logs of wood that were used to ram the wall or gate of a castle. The purpose of a battering ram was to shatter the weak spot of a castle and carve an opening point for the attackers.
A battering ram was typically covered in an iron roof to shield it from fire arrows. However, the defenders on the walls could still pour hot oil from above to prevent the men heaving the ram from reaching the wall.
A battering ram had an obvious advantage once it was close enough to a wall or a gate. However, it took considerable effort for the attackers to bring the ram this close.
Undermining tactics were used to compromise the integrity and strength of a castle’s walls. This was typically done by individuals who specialized in the task and known as sappers.
Sappers would get right next to the castle walls and start to pick out stones at the wall’s foundations. These served to weaken the structure.
Sappers needed to be protected by the attacking party from any missiles, arrows, or attacks from the wall’s defenders. They also had to look out for counter-measures from within the castle.
Defenders often dug mines of their own from the inside to counter the sappers and force them out of their mines by using smoke.