Medieval Catapults and Trebuchets

Recent reconstructions and computer simulations reveal the operating principles of the most powerful weapon of its time.

Scholars now generally agree that the successor states of the Roman empire in the early medieval West inherited two basic types of artillery from their imperial predecessors. The first of these consisted of torsion-powered engines (Roman: ballista, chieroballista, onager; Medieval: manga, mangonellus) that propelled their projectiles through the transformation of potential energy stored in twisted fibrous material, ranging from gut to horsehair and hempen rope, into kinetic energy that drove a wooden beam. The wooden beam, which could be equipped with a basket attached directly to the beam, or with a sling attached to its end, then transferred this kinetic energy to a projectile, usually a stone, located in the basket or sling. These engines generally were light artillery with rounds weighing 22–33 pounds (10–15kg). The second type of artillery available in late antiquity and throughout the Middle Ages was tension-powered. Tension engines (known as gastraphetes in the ancient world but balistae in the medieval world) used the same principle as handheld bows and crossbows, transferring the potential energy of the bow to the projectile, usually a long thin shaft equipped with an iron head, which looked like a large arrow or a crossbow bolt.

The range of engines (petraria, trubecheta, blida) that were probably the particular inventions of the Middle Ages employed the lever principle. Engines of this type were essentially long beams fixed to a fulcrum. The front, shorter end of the beam—i.e., the end closest to the target—is described by scholars as the target end, and the back, longer end is identified as the projectile end, because the projectile was attached there. Energy was generated by the rapid descent of the target end and the concomitant rapid rise of the projectile end.

Medieval engineers had two means of causing the rapid descent of the target end. The first method was to have a large number of well-trained men pull down, in unison, on ropes attached to the target end. Engines employing this method have been identified by scholars as a “traction type.” The traction lever engine was the only type of lever engine available in the Latin West and in the Levant until the end of the twelfth century.

The second method used to cause the rapid descent of the target end was to attach a very heavy weight to it. These weights, called trubae in some medieval sources, could weigh up to 220 pounds (1,000kg) and varied considerably in material composition and construction. In many cases, artillery engineers used large lead castings. However, wooden containers filled with stone, or even clay, were also fixed to the target end. The projectile end, in this type of engine, although substantially longer, was therefore much lighter than the target end. In order to use this engine, the artillerymen had to drag down the projectile end and secure it. After it was loaded, the projectile end was set free and the much heavier weight on the target end fell rapidly, causing the projectile end to rise rapidly with the result that the projectile was sent on its way. Engines equipped with weights on their target ends have been designated by scholars as “counterweight” lever engines. Counterweight engines did not appear in the Latin West until the first quarter of the thirteenth century.

The technology available to artillery engineers remained relatively static from the late Roman period through the end of the twelfth century. Although some scholars have questioned whether torsion or, conversely, traction-lever artillery was produced in the Middle Ages, it is now generally agreed that both types of propulsion were used consistently. Nevertheless, there is even at present controversy on this point because of the nature of the sources of information that deal with artillery in the period before c. 1200. One of the major problems faced by scholars, who have tried to identify the types of artillery actually deployed in late antiquity and the Middle Ages, is the lack of precision in the use of terminology in contemporary narrative sources. Many of the authors of historical narratives, in which artillery is discussed, were personally unfamiliar with military technology and used generic terms, such as instrumentum (instrument), machina (machine), ingenium (engine), and catapulta (catapult) to describe the weapons that were deployed. Many authors of narrative sources also used terms such as tormentum, scorpio, petraria, and onager, which may have had a technical meaning as a particular type of artillery. The lack of description for these weapons, however, makes it virtually impossible to determine whether they were torsion- or lever-powered, much less their specific characteristics, e. g., one-armed or two, wheeled or stationary. Finally, the narrative sources frequently used closely related terms, e.g., manga and mangonellus, without making clear if these terms refer to the same type or to different types of artillery.

Perhaps the most famous example of terminological confusion concerns the type of artillery known to modern readers as the trebuchet. The Latin version of this word begins to appear in medieval narrative sources in the thirteenth century. The first mention of a trubechetum in England, for example, occurs in the context of Prince Louis of France’s invasion of the island in 1216. Louis is reported to have brought a trubechetum with him to help conduct sieges. The thirteenth-century narrative sources, however, do not provide detailed information about the construction of the trubechetum. In light of this ambiguity, the English term trebuchet frequently has been used by scholars in a generic manner to refer to all lever-powered artillery from the ninth century onward. In fact, however, trebuchet was not used by contemporaries as simply another generic term for lever-powered artillery, but rather referred to a sophisticated technological improvement introduced by government officials to replace the older type of traction lever engine with a counterweight design. (The term for the counterweight engine as a whole may have been derived from the word truba, noted above, which some medieval authors used to designated counterweights.) Instead of deploying an engine that required dozens if not scores of well-trained men to operate, the trebuchet required only a small crew to lock the projectile end of the piece of artillery into position. It has been suggested by scholars that the counterweight engines could propel much heavier stones than their traction-lever cousins, with rounds weighing as much as 100–200 pounds (45–90kg), over distances of 328 yards (300m).

It is a happy coincidence that the first major development in the technology of artillery in many hundreds of years coincides with the survival of major new sources of information that shed significant light on how the trebuchet differed from earlier engines. The number of surviving administrative documents in England, where we have the best information about developments in the construction of artillery, increases dramatically for the period 1200 and after. These documents include large numbers of reports from engineers and military officials concerning the construction of artillery. This is significant because, unlike the contemporary authors of narrative sources, these engineers and officials were very familiar with military technology, and had a range of very precise terms to discuss the types of engines that they built. It is from these reports that it is possible to determine that the trebuchet was a relatively small type of counterweight lever artillery that began to be produced in England c. 1225. By the early 1240s, engineers in England began to build much larger counterweight lever artillery, which they at first designated as blidae, but then later simply referred to as engines (ingenia).

Cultural Significance

It is widely accepted by medieval military historians that sieges were the dominant form of warfare from the late Roman Empire until the massive introduction of gunpowder weapons at the end of the fifteenth century. The pursuit of politico-military objectives throughout this period required the capture, or the holding, of fortifications and major fortified cities. In the late antique West, the Roman government long maintained a monopoly on the ability to produce and deploy the sophisticated siege engines, particularly stone-throwers, that facilitated the reduction of these fortified places short of starving the population and garrison into submission or storming the walls with overwhelming numbers and concomitantly high rates of casualties. The late fourth-century Roman military officer and historian Ammianus Marcelinus emphasized in his works that barbarians were quite simply unable to capture Roman fortress towns, or even substantial forts, because they lacked “modern” technology. Attila the Hun likewise famously lacked sophisticated siege engines during his assault on the city of Orléans in the north of Gaul in 451 C.E., as his men were reduced to trying to pull down the walls stone by stone with hand tools. By contrast with the barbarians, the Christianized rulers of the Roman successor states devoted tremendous human, material, and financial resources both to producing artillery and to maintaining as well as improving the Roman military infrastructure of fortifications and fortified cities, that could withstand these engines. Indeed, medieval engineers engaged in an ongoing and increasingly expensive cycle of competitive development in the technology of siege engines and of fortifications. This pattern of military spending, what one might term part of the pre-modern “military industrial complex,” continued throughout the Middle Ages.

Stone-throwing engines were constructed of specially designed wooden pieces, iron clamps and bolts, ropes, slings, baskets, and, in the case of trebuchets, counterweights. All of these elements of the engines’ material construction had to be built or produced by highly trained specialists. Not every carpenter knew either the designs or the techniques necessary to build the wooden framework for a piece of artillery, much less all of the types of artillery deployed by his government. Similarly, not every blacksmith knew how to produce the fittings necessary to withstand the stresses of holding together an engine that could hurl hundreds of rounds of stone ammunition weighing 100–200 pounds (45–90 kg). In order to ensure that a sufficient number of the correct types of artillery were available at the right place at the right time in good working order, governments in late antiquity and throughout the Middle Ages required a thoroughly articulated logistical system supported by a well-financed and highly structured military administration.

The Norman and Angevin kings of England, like many other rulers in medieval Europe, employed a corps of specialists in the construction of artillery, including torsion, tension, and lever engines of both the traction and counterweight types. These specialists, identified in contemporary English administrative sources as engineers (ingeniatores), were among the most highly paid officers of the crown. Some of them even became substantial landowners as a result. Each of these engineers employed numerous carpenters, blacksmiths, ropemakers, leatherworkers, woodcutters, carters, sailors, and bargemen. To gain a mere glimpse of the effort required to sustain this work, one can note that the royal forests of England rang with the axes of woodsmen preparing thousands of logs to be shipped to London, Dover, Carlisle, and other towns that served as major production centers for hundreds of enormous wall-breaking engines, as well as the even more numerous smaller pieces of artillery used as antipersonnel weapons. The lead mines of Cornwall produced hundreds and hundreds of tons of lead that were carted or shipped out for use as counterweights. The hides of whole herds of cows were required to produce slings. Masons chipped and shaped tens of thousands of stones to be used as ammunition, some of which can still be found at the sites of medieval sieges. To these basic elements of construction, one might add the thousands of carts, wagons, barges, and ships that were required to transport these supplies, as well as the completed artillery and ammunition. It is also necessary to keep in mind the mountains of grain and other foodstuffs necessary to feed the animal and human personnel who undertook these transportation duties. In economic terms, the production of weapons, in general, and of artillery, in particular, was a big industry that employed many thousands of workers. In sum, if we are permitted, as modern politicians are, to see the commitment of resources as a gauge of the importance attached by the government to a particular program, it is clear that the kings of England, and they were certainly not alone, valued artillery, including the trebuchet, very highly indeed.

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