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The onager was a Roman siege engine that is a type of catapult that uses a torsional force, generally from twisted rope, to store energy for the shot. The onager consisted of a large frame placed on the ground to whose front end a vertical frame of solid timber was rigidly fixed. A vertical spoke that passed through a rope bundle fastened to the frame had a sling attached which contained a projectile. To fire it, the spoke or arm was forced down, against the tension of twisted ropes or other springs, by a windlass, and then suddenly released. As the sling swung outwards, one end would release, as with a staff-sling, and the projectile would be hurled forward. The arm would then be caught by a padded beam or bed, when it could be winched back again.〔Denny, Mark "The Physics Teacher" vol 47, p 574-578, December 2009〕 The onagers of the Roman Empire were mainly used for besieging forts or settlements. They would often be armed with large stones that could be covered with a combustible substance and set alight. They could be outranged by bows. In the Middle Ages (recorded from around 1200) a less powerful version of the onager was used that held the projectile(s) in a fixed bowl instead of a sling. Some have speculated that contemporary drawings depicting fixed bowls were intentionally misleading and that catapults at the time still used slings. Such deception would occur because, at the time, catapults were state of the art weapons of war and their exact operation and construction would be a closely guarded secret. It derived its name from the kicking action of the machine, similar to that of an onager (wild ass). This engine was sometimes called the ''mangonel'', although that name may have also been used for a variety of siege engines. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Onager (weapon)」の詳細全文を読む スポンサード リンク
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