Though the latter extract is not so positive in its wording as the one first given, it undoubtedly refers to engines that cast either stones or arrows against the walls, especially as the prophet previously alludes to other means of assault. One of the most authentic descriptions of the use of great missive engines is to be found in the account by Plutarch of the siege of Syracuse by the Romans, 214–212 B.C. Cæsar in his Commentaries on the Gallic and Civil wars, B.C. 58–50, frequently mentions the engines which accompanied him in his expeditions. The balistas on wheels were harnessed to mules and called carro-balistas. The carro-balista discharged its heavy arrow over the head of the animal to which the shafts of the engine were attached. Among the ancients these carro-balistas acted as field artillery and one is plainly shown in use on Trajan’s Column. According to Vegetius, every cohort was equipped with one catapult and every century with one carro-balista; eleven soldiers being required to work the latter engine. [Page 32] [Illustration: FIG. 20.--THE ACTION OF THE TREBUCHET. A. The arm pulled down and secured by the slip-hook previous to unhooking the rope of the windlass. B. The arm released from the slip-hook and casting the stone out of its sling. C. The arm at the end of its upward sweep.] [Page 33] Sixty carro-balistas accompanied, therefore, besides ten catapults, a legion. The catapults were drawn along with the army on great carts yoked to oxen. In the battles and sieges sculptured on Trajan’s Column there are several figures of balistas and catapults. This splendid monument was erected in Rome, 105–113, to commemorate the victories of Trajan over the Dacians, and constitutes a pictorial record in carved stone containing some 2,500 figures of men and horses. It is astonishing what a large number of catapults and balistas were sometimes used in a siege. For instance, at the conquest of Carthage, B.C. 146, 120 great catapults and 200 small ones were taken from the defenders, besides 33 great balistas and 52 small ones (Livy).[21] [21] Just previous to the famous defence of Carthage, the Carthaginians surrendered to the Romans ‘two hundred thousand suits of armour and a countless number of arrows and javelins, besides catapults for shooting swift bolts and for throwing stones to the number of two thousand.’ From Appian of Alexandria, a Greek writer who flourished 98–161. Abulfaragio (Arab historian, 1226–1286) records that at the siege of Acre in 1191, 300 catapults and balistas were employed by Richard I. and Philip II. Abbo, a monk of Saint Germain des Prés, in his poetic but very detailed account of the siege of Paris by the Northmen in 885, 886, writes ‘that the besieged had a hundred catapults on the walls of the town.’[22]