This scene, an illustration depicting the siege of Jerusalem, is from William of Tyre’s 14th Century “History” (Bibliotheque Nationale de France). It shows two trebuchets in use next to a wheeled siege tower. The trebs are fairly basically drawn, but show the main features – a box of rocks, a sling containing the projectile, bracing timbers on the uprights and a timber base.
An alternative approach was to build huge wooden towers to overawe the defences and enable others to attack them. The Vikings attacked Paris with one in 885–6. At Verdun in 985, the siege-tower was dragged by ropes passed around stakes close to the city wall, so that the oxen were moving away from the enemy. In 1087, a Pisan and Genoese expedition employed similar towers to capture Pantelleria. Such machines were not necessarily mobile. At the siege of Pont Audemar in 1123, Henry I built a tower, but it was only used to rain missiles into the castle, whose garrison had first to watch the burning of the town around them and the devastation of the countryside. At Coria in Spain in 1138, wooden towers acted as firing platforms, while at Bedford in 1224 the huge towers built for Henry III seem to have been used to mount various kinds of stone-throwers which deluged the walls with missiles. At Ma’arra on the First Crusade, the tower built by Raymond of St Gilles was clearly mobile, but its purpose again was to act simply as a fire-base to cover mining and assaults by ladder, which eventually carried the day. This was probably the intended purpose of the towers in the siege of Jerusalem in July 1099, but that of Godfrey was fortuitously brought up close to the wall and a bridge was improvised to make entry. Fully mobile siege-towers with drawbridges to launch an assault became a feature of important sieges, notably in the Holy Land where they were pre-eminent in the capture of the Muslim cities of the coast. Barbarossa used them in Lombardy, and Edward I attacked Bothwell castle in 1301 with a tower that had been transported in sections and was covered in hides against fire. In the West, towers continued to be important right down to the invention of cannons. At Lisbon, the Anglo-Norman force brought up a tower some 28m high and when this was destroyed, they deployed another one, 25m high, apparently built and commanded by a Pisan engineer; this proved to be the final straw for the garrison, which surrendered.
Such devices had very obvious limitations. The ground might be very unfavourable, as at ’Arqa on the First Crusade, where the city walls crowned a steep slope. In southern Italy, the relative isolation of inland places may have made it difficult to get siege-machinery to them. Even where the ground was generally suitable, it had to be smoothed and often ditches obstructed the route to the walls; at Jerusalem, the Count of Toulouse paid one penny for every three stones cast into the moat by the southern wall, while at Tortosa in 1148 a huge ditch 43m wide and 32m deep had to be filled. The clumsiness and weight of the towers meant that they needed to be built as close as possible to the point of attack. At Jerusalem in 1099, the defenders of the northern wall built up the walls, set up catapults and prepared beams and padding to repel the expected attack. The crusaders changed their assault point, and this was probably the decisive factor in the siege: near Zion Gate the Count of Toulouse had no room for manoeuvre and his tower was ultimately incapacitated by catapult attack and fire. A similar fate befell Bohemond’s tower in the attack on Durazzo in 1108. Fire was the great enemy; the successful machine at Lisbon was covered with wet hides, with the animal tails hanging down for maximum flow, while at Jerusalem Godfrey’s tower was soaked in vinegar against the defenders’ “Greek Fire”. During the siege of Tyre, the defenders built a war-crane on the city walls, which overtopped the crusader siegetowers and destroyed them by dropping incendiaries on to them. Siege-towers were remarkable structures, but they were not a certain solution to the problem of attacking fortifications. Terrain was often a problem and countermeasures by the besieged could destroy them. Above all, they were costly and justified only for major objectives.
Artillery capable of battering fortifications and defenders into surrender, known in Roman times, continued to be used. At the siege of Paris in 885– 6, mangana, catapulta and balistae are mentioned as hurling missiles. But these are only a few of the bewildering variety of words used by medieval writers to refer to siege engines. Unfortunately, their use is inconsistent and such descriptions as they give are confusing. Orderic tells us that at Brévol in 1092 a great machine was rolled up to the wall, which suggests a tower or penthouse, but adds that it hurled stones: it is possible that this was some kind of platform that accommodated a stone-thrower. Otto of Freising refers to a mangonel as a kind of balista, although this was a quite different kind of machine. The word petraria, rendered as perrier in French, is often, used but this merely means a stone-thrower. William of Tyre and Guillaume le Breton both clearly suggest that perriers were for heavy bombardment while mangana were lighter anti-personnel weapons, and the same notion about the latter is found in the Chanson de la Croisade Albigeoise.
Mangonella would seem to be only a diminutive of mangana; in Roman times this referred to a weapon that depended for power on torsion. The mangana was a machine with a single arm, whose bottom end was embedded in a massive horizontal winding of sinew: the arm was bent back against the torsion of the winding and, when released, flew forward against a robust frame, hurling a stone out of a cup or sling on its end. The crash of impact between arm and bar probably explains the nickname onager, “the mule”, for this machine. The missile was thus launched in an arc like the shell from a howitzer. The Roman balista was a crossbow-like weapon, but the “bow” consisted of two arms, each mounted in a vertically wound gathering of sinews, which provided the tension when the string was drawn to fire a bolt or ball: its trajectory would have been flat. The term balista in medieval sources generally refers to crossbows. Clearly related was the arcu-balista or later springald, a flat-trajectory weapon rather like a giant crossbow, which was widely used in sieges.
The traction-trebuchet was the dominant form of artillery in our period. It was a device that originated in China and was transmitted to Europe by about the ninth century via the Arab world. It was essentially a beam pivoted between two high uprights: when the beam was pulled at one end by a team of men, the other flew up until a missile was released in an arcing trajectory either from a cup or, more effectively, from a sling. The pulling end of the beam was by far the shorter, in a ratio of perhaps 1 : 5, and the efficiency of the engine was enormously enhanced by the use of a sling on the throwing end. This kind of lever artillery varied in size, which partly accounts for the inconsistency of the language used to describe it; broadly, it would seem that petraria and mangana indicate sizeable examples and mangonella and tormenta lesser ones. There is no reason to believe that the principle of torsion was forgotten, but the impact of the throwing beam must have put enormous strain on the structure of the onager, which would have had to be very heavy to last any time, and of extraordinary size and weight to throw a large missile: lever-action machines were probably lighter and more durable. Moreover, the technology of lever-artillery could be easily assimilated by a society in which increasingly complex machinery, such as water mills with pivoting wheels and gears, was becoming common. At the siege of Jerusalem in 1099, both Albert of Aachen and Tudebode report that the crusaders used machines powerful enough to throw captured spies into the city; in the case cited by Tudebode, the machine had a sling, which, together with the presumed power, strongly suggests a traction-trebuchet and implies that they were not a novelty.
