The word catapult is a generic term used to describe all ancient and medieval non-gunpowder propelled missile-throwing artillery. The first catapult may have been invented in the early fourth century BCE. In 399 in Syracuse, King Dionysius I, threatened by the Carthaginians and other enemies, assembled a large group of engineers to create an arsenal of weapons. Among these was the first non-torsion artillery piece, the gastraphetes. In essence the gastraphetes (which in Greek means “belly-bow”) was little more than a large, powerful, and flexible bow. The flexibility of the weapon came from the material of the bow itself, which was a composite of wood, horn, and animal sinew: a wood core covered by a tension layer of sinew in front and a compression layer of horn in the back. This, using a sinew bowstring, supplied the propulsive force to the missile.
It was, in fact, not much different, although larger, from the handheld composite bow, which by the fourth century BCE had been known for several centuries. However, the difference between the handheld weapon and the gastraphetes was its power, supplied by the latter’s elaborate stock apparatus. It consisted of a heavy stock, made in two sections. The lower section, the case, was fixed solidly to the bow. The upper section (or slider), of approximately the same dimensions as the case, fitted into a dove-tailed groove in the case and was able to slide freely back and forth. On each side of the case was a straight ratchet with two curved bars, or pawls, fitted into the ratchets and attached to a claw-like trigger mechanism. At the end of the stock was a concave rest that the operator placed against his stomach and, with the front of the bow fixed on the ground, allowed him to withdraw the slider, attach the string to the trigger, load a missile, and discharge it. A man could thus draw the bowstring and discharge a missile with much greater power than was possible with the traditional hand-drawn bowstring. The gastraphetes had a range of between 50 and 100 meters greater than the hand-drawn composite bow, which has been estimated to have had a maximum range of 500 meters. More importantly, the missile was launched at greater velocity so that few pieces of armor could withstand it, although it was probably still too weak to breach the walls of even earth-and-wood fortifications.
Non-torsion artillery technology spread quickly throughout the ancient world, and soon improvements were made to the design of the original gastraphetes. By about 360 BCE, winches had been added to the stock, allowing for easier and greater drawing power; this ultimately brought increased force, and therefore velocity, to the missile. A base was also added, increasing both the stability and size of the weapon. Still, non-torsion artillery continued to be limited in force and power, both of which remained dependent on the strength and flexibility of the bow. If these were exceeded the bow simply broke. While some gastraphetes were equipped to fire stone balls, most fired only heavy, arrow-shaped bolts that also limited the force of impact.
To increase the velocity of the projectile, making the gastraphetes more powerful, it was necessary to change both the bow and the size and type of missile fired. Increasing the power of the bow was achieved by replacing the single, flexible bow of the earlier weapon with two non-flexible arms set in “springs” made from sinew. The users of the gastraphetes were probably aware that it was the sinew in the bow’s composition that gave it its power, so by using the sinew to form tightly twisted “springs,” the power of the artillery could be increased. Apart from this development, the rest of the torsion catapult remained little altered from its non-torsion predecessor, with a heavy sinew string, slider, winch, ratchet apparatus, and trigger mechanism. The springs were the only significant change in technology, and this allowed for much more powerful devices firing missiles, now almost always stone, weighing from 13 to 26 kilograms, although stones as large as 162 kilograms are known to have been fired. When the bowstring was drawn back on a torsion catapult, the force was transferred to the sinew springs which, when the trigger was pulled, made the bow arms spring forward, discharging the missile. The short, stout arms were able to withstand a much greater force than the flexible bow of earlier devices and together with the use of stone balls as ammunition meant that this weapon was capable of breaching the walls of fortifications and towns.
It is believed that the first torsion-spring catapults were made by Macedonian engineers between 353 and 341 BCE and used afterwards by Philip II in his conquest of Greece. The technology then passed to Philip’s son, Alexander the Great, who used it in his conquest of Persia, the Middle East, Egypt, and India. Alexander seemed to have been particularly impressed by his catapults’ power and used them successfully to take towns, such as Tyre in 332 BCE, which would have been nearly impossible to conquer by other siege methods.
After Alexander’s death, torsion artillery technology, which had by then clearly supplanted non-torsion pieces, passed to his successors and from them to Carthage, Rome, and other lands. Over time, improvements to the mechanism were made to increase its flexibility, power, and range. Most important among these was the addition of washers to the springs, which meant that the distance that the arms of the catapult could be drawn back was easily adjusted. In this way the amount of force delivered to the missile at discharge could be varied: a close target could be struck by a looser tension on the springs, while a more distant target needed a tighter tension. The springs could also be loosed when not being used in military campaign, to keep from weakening the sinew from the constant stress of being tightly wound. Other important innovations were the addition of bronze coverings over the springs, which kept them dry during rain or river crossings, and tripod swivel mounts, which allowed for a rapid change of direction in discharging missiles. Improvements were also made in the operation of torsion catapults. Training and thorough practice in their use developed and actively encouraged by competitions between catapult operators. Training schools, especially those at Samnos, Ceos, and Cyanae, also resulted in increased skill in their use. Rhodian operators were particularly highly prized for their proficiency in catapult firing, and they were frequently employed by both Greece and Rome as mercenary artillery operators.
In the ancient world the most sophisticated artillery was made at Alexandria under the Ptolemies, and their machines were much sought after. It is highly plausible that both Carthage and Rome, during the First and Second Punic Wars, faced each other using Alexandrian catapults. This gave Alexandria the impetus to construct some highly experimental catapult models. One of the most curious examples was a chain-driven repeating catapult described by Philon in the last part of the third century BCE. In this machine, bolts were fed one at a time from a magazine into the slider trough by means of a revolving drum. The chain-link drive, operated by a winch, then fired the bolt and recocked the weapon by engaging the lugs on the chain links with a pentagonal gear. A trigger claw was locked and fired at the appropriate time by pegs mounted in the stock of the weapon, past which the slider moved. There were, however, many problems with this machine. First, because it was so elaborate, the need for it to be constantly repaired must have been great. Second, it fired only along fixed lines, and thus would have been useful only against fixed targets, like a fortification wall. There is, in fact, no indication that this weapon was ever constructed, and it may indeed have been only an engineer’s dream design.
The Romans made two important alterations to the traditional torsion catapult—which they called a ballista. First, they made it smaller and more portable. Known as the cheiroballistra, this variation of the older torsion model contained all of the former’s parts and was probably not too much lighter. It was, however, more compact, easier to assemble, and easier to transport. In addition, the springs were set farther apart, giving a wider field of view, which made aiming easier. The bow arms seem to have been capable of greater range than larger torsion artillery. Clearly, this weapon was meant to be used on the battlefield, or at sea, rather than against fortifications.
The second alteration to the traditional ancient torsion catapult was more extreme. Rather than simulating a bow using two vertical sinew springs with two arms swinging horizontally, the onager used only one horizontal spring and one arm swinging upwards. There was no bowstring; at the end of the single arm was a sling in which a missile, presumably a stone ball, could be placed for launching. The trigger was a piece of rope used to anchor the arm for loading. The arm was mounted on two large, heavy main horizontal beams held apart by a number of crossbeams. The onager was much more like our modern perception of a catapult than other ancient models. However, it should be noted that this weapon was infrequently used by the Romans, who continued to prefer traditional torsion artillery. Apparently, it appeared only at the end of the Empire and is mentioned only by one author, Ammianus Marcellinus (330–390 CE).
That torsion catapults were effective in sieges and on the battlefield is without question. Although their range seems not to have differed much from nontorsion catapults or even from strong bowmen without a substantial decrease in accuracy—most stone-throwing artillery needed to be within 150 meters of a fortification to be effective—the force of impact of a missile fired from one of these weapons was astonishing. At the siege of Gaza, Alexander the Great was wounded in the neck by a catapult bolt that pierced both his shield and his breastplate. A skull unearthed at Maiden Castle in Dorset was pierced by a catapult bolt moving at such a high velocity that it did not smash it; had the missile been an arrow from a handheld bow, the skull would surely have shattered. Perhaps the most vivid picture of the awe-inspiring power of these weapons comes from the pen of Josephus, the Jewish historian of the first-century Roman conquest of rebellious Judea, who details their use by the Romans at the siege of Jotapata in 67 CE:
The force with which these weapons threw stones and darts was such that a single projectile ran through a row of men, and the momentum of the stones hurled by the engine carried away battlements and knocked off corners of towers. There is in fact no body of men so strong that it cannot be laid low to the last rank by the impact of these huge stones.… Getting in the line of fire, one of the men standing near Josephus [the commander of Jotapata, not the historian] on the rampart had his head knocked off by a stone, his skull being flung like a pebble from a sling more than 600 meters; and when a pregnant woman on leaving her house at daybreak was struck in the belly, the unborn child was carried away 100 meters.
When the barbarian tribes invaded the Roman Empire in the fourth and fifth centuries, they were met by an enemy using artillery—ballistae, cheiroballistae, and onagers. Indeed, the Romans might have had catapults to defend nearly every fortification besieged by the invaders, and it is reported that several arms factories continued to supply artillery pieces for military use during the early invasions. It is similarly recorded that in some engagements these catapults were successful in thwarting barbarian attacks. For example, Ammianus Marcellinus describes how one attack by the Goths was halted when a single large stone fired from an onager, despite hitting no one, caused such mass confusion that the attackers were routed. And Procopius, writing about the defense of Rome in 537–38, provides a colorful witness to catapult destruction:
… at the Salerian Gate a Goth of goodly stature and a capable warrior, wearing a corselet and having a helmet on his head, a man who was of no mean station in the Gothic nation… was hit by a missile from an engine which was on a tower at his left. And passing through the corselet and the body of the man, the missile sank more than half its length into the tree, and pinning him to the spot where it entered the tree, it suspended him there a corpse.
Ultimately, however, even with the use of catapults, the Roman armies could not withstand the barbarian invaders. Indeed, it seems likely that there were many problems with their technology and use. First, many towns and fortifications probably did not have a large arsenal of catapults at the beginning of the barbarian invasions. After all, most western imperial towns had been very secure for a long time and had rarely, if ever, been threatened. Second, at this time many military detachments seem to have been unfamiliar with catapults and untrained in their use, a fact attested to by many contemporary authors. Finally, many of these machines were probably not in good working order. It has been estimated that the life of sinew springs was no more than eight to ten years, and many of the existing artillery pieces undoubtedly had strings that did not function properly.