Torsion siege engine

Traditional historiography puts the speculative date of the invention of two-armed torsion machines during the reign of Philip II of Macedon circa 340 BC, which is not unreasonable given the earliest surviving evidence of siege engines stated above.

[14] The Greeks and Romans, with advanced methods of military supply and armament, were able to readily produce the many pieces needed to build a ballista.

In the later 4th and 5th centuries as these administrative structures began to change, simpler devices became preferable because the technical skills needed to produce more complex machines were no longer as common.

Vegetius, Ammianus Marcellinus, and the anonymous "De rebus bellicis" are our first and most descriptive sources on torsion machines, all writing in the 4th century AD.

[16] A common misconception about torsion siege engines such as the ballista or onager is their continued usage after the beginning of the Early Middle Ages (late 5th-10th centuries AD).

The myth of the torsion mangonel began in the 18th century when Francis Grose claimed that the onager was the dominant medieval artillery until the arrival of gunpowder.

In the mid-19th century, Guillaume Henri Dufour adjusted this framework by arguing that onagers went out of use in medieval times, but were directly replaced by the counterweight trebuchet.

[19] The torsion mangonel myth is particularly appealing for many historians due to its potential as an argument for the continuity of classical technologies and scientific knowledge into the Early Middle Ages, which they use to refute the concept of medieval decline.

He proposed that all medieval terms for artillery actually referred to the trebuchet, and that the knowledge to build torsion engines had been lost since classical times.

[21] In 1941, Kalervo Huuri argued that the onager remained in use in the Mediterranean region, but not ballistas, until the 7th century when "its employment became obscured in the terminology as the traction trebuchet came into use.

[24] However by the 9th century, when the first Western European reference to a mangana (mangonel) appeared, there is virtually no evidence at all, whether textual or artistic, of torsion engines used in warfare.

[28] ... anyone consulting Bradbury’s Routledge Companion to Medieval Warfare (2004) will find mangonels described as stone-throwing catapults powered by the torsion effect of twisted ropes...

In all this mass of illustrations, there are numerous depictions of manually operated stone throwers, then of trebuchets and, finally, of bombards and other types of weapon and siege equipment.

Taking into consideration the constraints under which the monastic artists were working, and their purpose (which was not, of course, to provide a scientifically precise depiction of a particular siege), such illustrations are often remarkably accurate.

Torsion power went out of use for some seven centuries before returning in the guise of the bolt-throwing springald, deployed not as an offensive, wallbreaking siege engine, but to defend those walls against human assailants.

For example at the end of the 19th century, Gustav Köhler contended that the petrary was a traction trebuchet, invented by Muslims, whereas the mangonel was a torsion catapult.

[35] Even in this instance it is never stated that the machine was torsion, as was the case with uses of other terminology such as mangana by William of Tyre and Willam the Breton, used to indicate small stone-throwing engines, or "cum cornu" ("with horns") in 1143 by Jacques de Vitry.

[42] Further design modifications that became standard include combining the two separate spring frames into a single unit to increase durability and stability, the addition of a padded heel block to stop the recoil of the machine,[43] the development of formulae to determine the appropriate engine size (see Construction & Measurements below), and a ratcheting trigger mechanism that made it quicker to fire the machine.

Marsden's description of torsion machine development follows the general course that Heron of Alexandria lays out, but the Greek writer does not give any dates, either.

[48] The preferred type of sinews came from the feet of deer (assumedly achilles tendons because they were longest) and the necks of oxen (strong from constant yoking).

[51] Landels additionally argues that the energy-storing capacity of sinew is much greater than a wooden beam or bow, especially considering that wood's performance in tension devices is severely affected by temperatures above 77 °F (25 °C), which was not uncommon in a Mediterranean climate.

[55] The only way to do so would be to construct a whole range of full-scale devices using period techniques and supplies to test the legitimacy of individual design specifications and their effectiveness of their power.

Kelly DeVries and Serafina Cuomo claim torsion engines needed to be about 150 m (490 ft) or closer to their target to be effective, though this is based on literary evidence, too.

"[59] The obvious disadvantage to any device powered primarily by animal tissue is that they had the potential to deteriorate rapidly and be severely affected by changing weather.

This prevented damage to the skein, increased the structural integrity of the frame, and allowed engineers to precisely adjust tension levels using evenly spaced holes on the outer rim of the washers.

[62] What is known is that they were used to provide covering fire while the attacking army was assaulting a fortification, filling in a ditch, and bringing other siege engines up to walls.

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 m (2,000 ft); and when a pregnant woman on leaving her house at daybreak was struck in the belly, the unborn child was carried away 100 m (330 ft).

"[69] "...at the Salerian Gate a Goth of goodly statue 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 this left.

[71] The list below provides terms that have been found in reference to torsion engines in the ancient and medieval eras, but their specific definitions are largely inconclusive.