A mangonel was a type of medieval catapult or siege engine used to throw projectiles at or over a castle's walls. While not particularly accurate, Mangonels were capable of firing projectiles up to 400 meters, nearly as far as a trebuchet (which were introduced later, shortly before the discovery and widespread usage of gunpowder).

The Mangonel, or Onager, is a type of catapult which saw widespread use throughout the medieval period. The Romans were the first to use this type of catapult. The word Mangonel is derived from the Latin word manganon which means “an engine of war”. Mangonels were also referred to as Onagers or Scorpions, due to the similarities between these animals' anatomy or motion and the structure and firing mechanisms of the Mangonel. The word Onager refers to a type of donkey, whose kicking motion and force were paralleled in the Mangonel. The Mangonel's firing motion resemble the kick of an onager, and the Mangonel's firing arm and hook resemble a Scorpion's tail and stinger. Mangonels fired heavy projectiles from a bowl-shaped bucket at the end of the firearm. The Mangonel's power is derived from twisted sinew ropes, similar to those in a Ballista, however a Mangonel only has one arm as opposed to the Ballista's two. The Mangonel's maneuverability was greatly improved by the Romans who added wheels to its base. The addition of wheels and the Mangonel's light weight made it easy to move. In combat, Mangonels hurled rocks, burning objects (or vessels filled with flammable materials which created a fireball on impact), or anything else readily available to the attacking force. One of the more unusual types of projectile was that of dead, and often partially decomposed, carcasses of animals or people. These were used to intimidate the defending force, lower their morale, and often to spread disease amongst the besieged. This tactic often proved effective as the short supply of food, which was often low quality or rotting, combined with the cramped living space of the defenders, poor hygiene, and infestations of vermin (which made convenient vectors for disease) made the ideal scenario for the spread of disease.

In addition to laying waste to enemy castles during sieges, the Mangonel was also eventually adapted to provide cover for troops on the battlefield. This tactic was first devised and employed by Alexander the Great.

Despite its lack of accuracy, the versatility and maneuverability of the Mangonel ensured that it was the premiere siege catapult used during the medieval period.