Siegebeasts were large Hollow-dwelling creatures that appeared in the Gears of War video game series. Like many species of the Hollow, they have a peculiar biology that humans have yet to understand. The Locust Horde have enslaved these beasts and use them as living artillery platforms, hence their name.
The Siegebeast is a creature enslaved by the Locust for use as an artillery piece. It has been mounted on a carriage for better mobility, and to stop it from turning on its masters. Its head is still exposed though, and will bite anything close to it. It is armed with a giant catapult on its back made from its own limbs. It also appears to be a totally self-sufficient weapon. To prepare it for firing, the large appendages at the front are wound back and held in position, then a canister on its back opens and deposits a large ball of explosive, organic matter into the cup on the end of the wound limbs. The cupped limbs are then released, creating a huge amount of energy, firing the explosive ordinance accurately, even at long ranges. It can cause devastating damage to King Raven helicopters, or even a Brumak when hijacked by COG Gears.
It is unknown how or if the Siegebeasts were affected by the Imulsion Countermeasure device that was fired at the end of the Locust War, though the remains of Siegebeasts have been discovered in the years since that have not been crystallized in the same manner as the Locust. It is currently unknown if any Siegebeasts survived after the war.