The Monster Mortar () was one of the largest mortars ever developed. Also called Leopold or the Liège mortar, the caliber mortar was conceived by the French artillery officer Henri-Joseph Paixhans. The mortar was manufactured under the direction of the Belgian Minister of War Baron Louis Evain and cast at the Royal Canon Foundry (Fonderie royale de canons) in Liège, Belgium in 1832. It saw action at the Battle of Antwerp in December 1832.
