ram, such as a large sack of sawdust, just before the ram's head struck a wall or gate, or by using grappling hooks to immobilize the ram's log. Alternatively, the ram could be set ablaze, doused in fire-heated sand, pounded by boulders dropped from battlements or invested by a rapid sally of troops. Some battering rams were not slung from ropes or chains, but were instead supported by rollers. This allowed the ram to achieve a greater speed before striking its target, making it more destructive. Such a ram, as used by Alexander the Great, is described by Vitruvius. Alternatives to the battering ram included the drill, the sapper's mouse, the pick, the siege hook, and the hunting ram. These devices were smaller than a ram and could be used in confined spaces. Notable sieges Battering rams had an important effect on the evolution of defensive walls, which were constructed ever more ingeniously in a bid to nullify the effects of siege engines. Historical instances of the usage of battering rams in sieges of major cities include: The destruction of Jerusalem by the Romans The Crusades The Sack of Rome (410) The various sieges of Constantinople There is a popular myth in Gloucester, England that the well known children's rhyme, Humpty Dumpty, is about a battering ram used in the siege of Gloucester in 1643, during the Civil War. However, the story is almost certainly untrue; during the siege, which lasted only one month, no battering rams were used, although many cannons were. The idea seems to have originated in a spoof history essay by Professor David Daube written for The Oxford Magazine in 1956, which was widely believed despite obvious improbabilities (e.g., planning to cross the River Severn by running the ram down a hill at speed, although the river is about 30 m (100 feet) wide at this point). Modern use Battering rams still have a use in modern times. Police forces often employ small, one-man or two-man metal rams, known as enforcers, for forcing open locked portals or effecting a door breaching. Modern battering rams sometimes incorporate a cylinder, along the length of which a piston fires automatically upon striking a hard object, thus enhancing the momentum of the impact significantly. See also Aerial ramming – In military aviation, deliberately causing a mid-air collision to attack an opposing aircraft Impact (mechanics) List of siege engines Naval ram