Seige

A seige tower is designed to let the attacker try to enter a fortification by crossing over its wall.

The term seige or beseige refers to the military techniques for surrounding an enemy protected by a fortification.

A seige can cut off the enemy's supply of fresh food, water, and other essential supplies. The beseiging force can defeat their enemy by waiting until they run out of food, and surrenders.

In recent millenia seige engines began to be employed, that could attack enemies even within their fortifications. These included catapults, trebuchets and ballista.

Sometimes beseigers would build towers, on wheels, that could be pushed up against the enemy's walls, so beseigers could fight their way inside, by crossing over the top of the walls.

If the garrison of the fortification were numerous enough, and well armed enough, they could fire upon any beseigers who tried to get close enough to undermine the integrity of the fortification's walls. So techniques were developed to dig zig-zag trenches, so beseigers could get close enough to undermine a wall. Alternatively, miners would tunnel up to and under a wall.