A military engine for hurling missiles of any kind. All the missiles used in war, except those thrown from the sling (see Funda), were projected either by the hand alone or with the aid of elastic substances. Of elastic instruments, the bow (see Arcus) was used by all ancient nations. The tormentum was so called from the twisting (torquendo) of hairs, thongs, and vegetable fibres; and the word is often used by itself to denote engines of various kinds; often, also, these engines are specified separately under the names of ballistae and catapultae, which names, however, most commonly occur together in the accounts of sieges and other military operations, because the two kinds of engines denoted by them were almost always used in conjunction. (See Helepolis.) The ballista (πετροβόλος) was used to shoot stones, the catapulta (καταπέλτης, καταπελτική) to project darts, especially the falarica (q. v.), and a kind of missile four and a half feet long, called trifax. While, in besieging a city, the ram (see Aries) was employed in destroying the lower part of the wall, the ballista was used to overthrow the battlements (propugnacula), and the catapult to shoot any of the besieged who appeared between them. The forms of these machines being adapted to the objects which they were intended to throw, the catapult was long, the ballista nearly square, which explains the following humorous enumeration by Plautus ( Capt.iv. 2 Capt., 16) of the three μηχαναί, the application of which has just been explained:
Meus est ballista pugnus, cubitus catapulta est mihi,
In the same armament the number of catapults was commonly much greater than the number of ballistae. Also, these two classes of machines were both of them distinguished into the greater and the less, the number of the less being much more considerable than the number of the greater. When Carthago Nova, which had served the Carthaginians for an arsenal, was taken by the Romans, the following were found in it: 120 large and 281 small catapults; 23 large and 52 small ballistae. Three sizes of the ballista are mentioned [figure in text: Ballista. (Baumeister.)] by historians, (a) that which threw stones weighing half a hundredweight (τριακονταμναίους λίθους), (b) a whole hundredweight (ballista centenaria, λιθοβόλος ταλαντιαίος), and (c) three hundredweight (πετροβόλος τριτάλαντος). Besides these, Vitruvius (x. 11) mentions many other sizes, even down to the ballista which threw a stone of only two pounds' weight. In like manner, catapults were classified according to the length of the arrows shot from them. According to Iosephus, who gives some remarkable instances of the destructive force of the ballista, it threw stones to the distance of a quarter of a mile (Bell. Iud. iii. 7, 19-23). Neither from the best-known authors nor from the figures on the Column of Trajan are we able to form a very exact idea of the construction of these engines. Still less are we informed on the subject of the scorpio or onager, which was also a tor- [figure in text: Onager or Scorpio. (Marquardt.)] mentum. The best notion of ancient artillery is to be gathered from the treatise of Hero (Βελοποιϊκά), [p. 1593]
and that of Philo (Περὶ Βελοποιϊκῶν), both written in the second or third century B.C.
The various kinds of tormenta appear to have been invented shortly before the time of Alexander the Great. When horsehair and other materials failed, the women in several instances cut off their own hair, and twisted it into ropes for the engines. (See Punic Wars.) These machines, with those who had the management of them, and who were called ballistarii and ἀφεταί, were drawn up in the rear of an advancing army, so as to throw over the heads of the front ranks. In order to attack a maritime city, they were carried on the decks of vessels constructed for the purpose ( Diod. Sic.xx. 83-86).
Both of the chief varieties of tormenta were based upon the principle of the crossbow; but the elasticity of the bow was exchanged for elasticity in the twist of the cord. Consequently, as explained above, all pieces of heavy artillery were called by the Romans tormenta. The machine consisted of three parts: the stand, the groove for the shot, and the apparatus representing the bow. This consisted of a frame in three divisions, through the midmost of which passed the groove for the shot. In each of the lateral divisions was stretched, in a vertical direction, a set of strong elastic cords, made of the sinews of animals, or the long hair of animals or of women. These were stretched tight, and between each of them was fixed a straight unelastic arm of wood. The arms were joined by a cord, which was pulled back by a winch applied at the end of the groove. On letting this go, the arms, and with them the string and the object in front of it, were driven forward by the twisting of the vertical cords. The effectiveness of the engine thus depended on the [figure in text: Catapulta.] power and twist of the cords, which may be said roughly to express its calibre. The engines were divided into two kinds, (1) catapultae, or scorpiones. In these the groove for the shot was horizontal, and they projected missiles of length and thickness varying according to the calibre;
(2) ballistae, which shot stones, beams, or balls up to 162 lbs. weight, at an angle of 50 degrees. The calibre of the ballista was at least three times as great as that of the catapult. The average range of the catapult was about 383 yards, that of the ballista from about 295 to 503 yards.
After Constantine we hear no more of catapults, but only of ballistae and the onager. The ballista now shot arrows, and is described either as a huge cross-bow with an elastic bow of iron, or as virtually identical with the old catapult. The onager, also called scorpio, was a sling for stones, consisting of a frame in which was fastened a sort of wooden arm with a sling at one end.
As a rule, the heavy artillery was employed only in sieges; but artillery accompanied armies in the field for purposes of conquest or defence. The legions and the cohorts of the Praetorian Guard had their own artillery, and at the end of the fourth century every centuria in the legion had a ballista of the later kind drawn on wheels by mules (carroballista), and served by eleven men. Every cohort had an onager, carried on a cart drawn by two oxen. See the article by A. Mller in Baumeister's Denkmler, s. v. Festungskrieg und Belagerungswesen, i. pp. 525 foll.; Droysen, Die griechischen Kriegsalterthmer, pp. 187-204; Wescher, Poliorctique des Grecs (1867); and Rstow and Kchly, Geschichte des griechischen Kriegswesens (1852).