Onager (weapon) Onager (weapon) The onager (British /ˈɒnədʒə/, /ˈɒnəɡə/, U.S. /ˈɑnədʒər/) was an imperial-era Roman torsion powered siege engine; in other words, a small catapult. The onager was first mentioned in 353 AD by Ammianus Marcellinus, who described onagers as the same as a scorpion. According to two authors of the later Roman Empire who wrote on military affairs, the onager derived its name from the kicking action of the machine that threw stones into the air, as did the hooves of the wild ass, the onager, which was native to the eastern part of the empire. The onager consisted of a
Onager (weapon) could be winched back again. 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. The onager was used from the 4th century AD until the 6th century AD. The late-fourth century author Ammianus Marcellinus describes 'onager' as a neologism for scorpions and relates various incidents in which the engines fire both rocks and arrow-shaped missiles. The late-fourth or early-fifth century military writer Vegetius stipulates that a legion ought to field ten onagers, one for each cohort.