Besieger (noun)

A person or army that lays siege to a fortified place in order to capture it.

Origin:

Late middle english, from old french, from besiegier, from siège siege.

Examples:

1. The city was under siege by the enemy army for several months.
2. The besieger used all means at their disposal to break through the walls.
3. The besiegers were eventually forced to abandon the siege due to lack of supplies.
4. The castle was considered impregnable, but the besiegers finally succeeded in capturing it.
5. The besieger's tactics included digging tunnels beneath the walls and mounting surprise attacks.