Medieval Torsion Catapults

[D B Campbell]

according to widely accepted view, the word mangonel is derived from Greek word, manganon, literally means engine of war.

Greek μάγγανον (manganon) actually means a "conjuror's magical trick". It only comes to mean "engine of war" by adding the adjective πολεμικόν (polemikon, "of war") to it. The machine is thus "a miracle of war"!

[Koyuncu]

That should be fixed in some numerous books in that case. Thanks for correction. Apparently onager finally got the name it really deserves.

In case of silk as spring material, that is only mentioned in Eastern Roman manuals while in west, horse hair is used mostly. There are large quantities(tens of pounds) of horse hair in purchase lists of armies in Western Europe.

[D B Campbell]

Espringals often used silk skeins to power the bow arms, which might have been an improvement.

I would doubt whether silk could be an improvement on sinew. It's elasticity characteristics are completely different. Consider why a bow-string can be made of silk: precisely because, like linen, it has a low energy storage capacity, which allows most of the energy to be transferred successfully into the missile. This is precisely the opposite of what is required in a torsion spring. (Like linen, silk also has a high tensile strength, meaning that it tolerates higher tractive stress -- exactly what you want in a bowstring.)

In case of silk as spring material, that is only mentioned in Eastern Roman manuals while in west, horse hair is used mostly.

I would be interested to see where your information on silk has come from. Greek and Roman catapults used animal fibre for the torsion springs (ideally, sinew; otherwise horsehair; at a pinch, human hair) because of the peculiarities of its elasticity. Silk (similar to plant fibre) has nothing like the elasticity of animal fibre.

[Koyuncu]

From, SIEGECRAFT, Two Tenth-Century Instructional Manuals by “Heron of Byzantium” Denis F. Sullivan

In the book Medieval Siege Weapons (2): Byzantium, the Islamic World and India AD 476-1526, David Nicolle, mentions some Arabic espringals using silk skeins in torsion springs. It is probable that this could influence Eastern Roman engineers to use them too.

I have zero knowledge about Greek language but if silk is used as bow strings maybe it was used in same way for machines. Then it is probable that this issue is actually a translation error.

[D B Campbell]

I have zero knowledge about Greek language but if silk is used as bow strings maybe it was used in same way for machines.

You are undoubtedly correct. The bowstring on a catapult is just a bigger version of the bowstring on a hand-bow. But the torsion-springs are quite a different matter!

[Urselius]

Espringals often used silk skeins to power the bow arms, which might have been an improvement.

I would doubt whether silk could be an improvement on sinew. It's elasticity characteristics are completely different. Consider why a bow-string can be made of silk: precisely because, like linen, it has a low energy storage capacity, which allows most of the energy to be transferred successfully into the missile. This is precisely the opposite of what is required in a torsion spring. (Like linen, silk also has a high tensile strength, meaning that it tolerates higher tractive stress -- exactly what you want in a bowstring.)

In case of silk as spring material, that is only mentioned in Eastern Roman manuals while in west, horse hair is used mostly.

I would be interested to see where your information on silk has come from. Greek and Roman catapults used animal fibre for the torsion springs (ideally, sinew; otherwise horsehair; at a pinch, human hair) because of the peculiarities of its elasticity. Silk (similar to plant fibre) has nothing like the elasticity of animal fibre.

Well sinew can also be used for making bowstrings. The properties of a protein-based fibre as a single string and when used in a skein of multiple strings are different. I'm sure that a skein of Bombyx silk would have considerable elasticity and energy-storage abilities. Also I imagine that it might have a much greater toleration of variations in environmental moisture levels than sinew and perhaps horse-hair, giving it more relaible performance.

[Flavivs Aetivs]

Spider silk is pretty elastic fantastic, don't know how silkworm silk is though. Obviously the Romans/Chinese didn't harvest spiders to create their silk.

[D B Campbell]

Well sinew can also be used for making bowstrings. ... I'm sure that a skein of Bombyx silk would have considerable elasticity and energy-storage abilities.

The Greek writers often refer to a bow-string as a νευρά (neura; literally, sinew-cord). It is true that sinew can be used to manufacture a bow-string, but it will not be ideal, because of its elasticity. It's possible that the ancients thought some degree of elasticity to be desirable in their bow-strings, but (afaik) none of them ever explains this (slings could also be manufactured from elastic material). It is interesting that, as soon as silk became available, archers quickly adopted it.

The point here is that the reverse is not true. Torsion springs require maximum elasticity in order to store energy. Bow-strings do not. You can make torsion-springs out of any kind of cord, but torsion-springs made of silk would be far inferior to hair springs, which in turn are far inferior to sinew springs. You suggested that silk springs might be an improvement on sinew. I believe that they would not be.

[Urselius]

Mardi bin Ali al-Tarsusi, the 12th century Arab author, describes torsion powered bolt-firing artillery having skeins made of a mixture of silk and horsehair.

[D B Campbell]

... artillery having skeins made of a mixture of silk and horsehair.

Interesting. (Horsehair, of course, is no surprise. But the two materials stretch at different rates, making a mixture somewhat puzzling.)

[Koyuncu]

Mardi bin Ali al-Tarsusi, the 12th century Arab author, describes torsion powered bolt-firing artillery having skeins made of a mixture of silk and horsehair.

I already noted that too.

In the book Medieval Siege Weapons (2): Byzantium, the Islamic World and India AD 476-1526, David Nicolle, mentions some Arabic espringals using silk skeins in torsion springs. It is probable that this could influence Eastern Roman engineers to use them too.

Here the related part of book; http://books.google.com.tr/books?id=ybcl...on&f=false

Here a detailed description about qaws al ziyar;

The ziyar was a torsion siege weapon. Its twisted ropes or skeins were made of animal tendons, animal hair, or silk. Used from at least the 12th century, it was either single armed or double armed. Saladin's men effectively used ziyars during the siege of Acre in the Third Crusade (1189–92). In the 13th and 14th centuries the ziyar was used in Morocco and was sufficiently small and portable that one single ox cart could carry four siege weapons. It was used to throw stones or semiexplosive incendiary material. The bow ziyar, qaws al-ziyar, could shoot large arrows.

Saladin as prime minister, or vizier, of Ayyubid Egypt commissioned a military treatise by Mardi al-Tarsusi in approximately 1169 that described a gigantic two-armed torsion-powered siege weapon called the qaws al-ziyar and known in Europe as an espringal. According to al-Tarsusi's Tabsirat arbab al-albab fi l-najat fi l-hurub (Instruction of the valiant on prevailing in war), the frame for this weapon was gigantic, over 16 1/2 feet tall. It had strings or skeins of mixed silk and horse hair. The frame was made of unseasoned oak. The draw weight weighed one and a half tons. Even without the windlass, Mardi al-Tarsusi explained that 20 men were needed to pull back its bow string.

From; http://books.google.com.tr/books?id=-Jf5...ar&f=false

Also, I tried to search Three Byzantine Military Treatises by George T. Dennis but failed to find silk torsion springs mentioned in The Anonymous Byzantine Treatise on Strategy. How Dennis F. Sullian get the information about it is unknown.

[Eleatic Guest]

]...gigantic two-armed torsion-powered siege weapon ...The draw weight weighed one and a half tons. Even without the windlass, Mardi al-Tarsusi explained that 20 men were needed to pull back its bow string.

Evidently the modern author infers a draw weight of 1.500 kg by assuming 75 kg per person. This is highly interesting. Do we have data on the draw power of ancient catapults/ballistae, either derived from ancient sources or won through experimental archaeology?

PS: Seems like one Liebel in Springalds and Great Crossbows (Royal Armouries Monograph, 1998) did some calculations. He arrives at 800 pounds for a cheiroballistra and nearly 4.000 pounds draw power for a springald.

[D B Campbell]

Mardi bin Ali al-Tarsusi, the 12th century Arab author, describes torsion powered bolt-firing artillery having skeins made of a mixture of silk and horsehair.

I note that you have taken your information from David Nicolle's Osprey book about medieval siege weapons. I did a little digging and found the relevant text:
[attachment=8396]BodleianHunt264.jpg[/attachment]

Unfortunately, I do not read Arabic, but I post it here in case someone else would like to have a stab at deciphering it. Meanwhile, I located a French translation of the relevant section (http://www.jstor.org/stable/41603236), which proved rather interesting. Far from being "torsion-powered bolt-firing artillery", the machine in question appears to be a giant composite bow of the sort normally referred to as a "non-torsion catapult".

Here is my rough translation of the French translation (!) of the Arabic text:

Start by making a bow with two leaves of green oak wood each six cubits long, and more than a span and a half broad, and an average of a span wide. The top of each leaf is approximately a twelfth of the qa’ida. They are lined with horn and glue in autumn, bound as bows are bound, and left until their time is up and there is a guarantee of adhesion of the glue against any separation. This completed, we attach the gut after having sorted out the wood and removed all its bumps with a file, and likewise levelled out the horn with a file in the usual manner. The opposition of the gut should in every detail in a number of hands (?) be proportionate to the bow, and should be allowed to dry perfectly for a long time, and then tidied up with the file, as we do with bows, and polished up until the roughness disappears and perfect symmetry is obtained. When this is completed, we coat the outside tûz as we do with Arab bows; and if you want to gild, embellish, or polish with varnish of firâgh, which is the most beautiful for this purpose, that’s your concern, and if you want to polish the tûz with the same varnish, without any ornament or gilding, that’s your business. Finally, we make in the sides of the bow the usual notches for the string, and they have roughly the thickness so that this string will pass through.

Thus far, a giant composite bow.

There should be a sort of square with four sides of green oak wood of good quality, or of another wood in its place, which we will level and plane down more perfectly; each side will have a length of ten cubits, more or less, depending on the dimensions of the bow. We put in the middle of the square a cross-member, thick and wide, fixed in terms of the height, with a well formed opening fitted with two doors, each made of a sheet of iron, of which part should be on an axis in its upper part (?), when we leave the lid, and which open when the arrow lifts it to discharge; the width of this opening must therefore be proportionate to that of the arrow, and a little greater. On both sides of this cross-member you must put two strips of green oak wood that are fixed side by side. There is then braided, around the top and bottom sides of the square, approximately two thirds of the way from the middle of the cross member, a net (ziyâr) of horsehair and silk, in which each thread has the thickness of a little finger; likewise the string (watar) that stretches the bow should be proportionate, and, if its strength is a qintâr, it should weigh fifteen dirhams, and increase or decrease with it.

This seems to be a large wooden frame, designed to carry the giant bow, which has not yet been installed in it.

Then the net (ziyâr) in question is wound around pitons of boxwood to the other one, on both sides, until it is well stretched; these pitons must be big for when the torsion around them reached its maximum; and that [ illegible Arabic words ] their location has the width of the leaf of the bow when it is in place.

Further description of the horsehair-and-silk "net", which is wound around wooden pitons, seemingly at the top and bottom of the frame.

And then we remove (?) these pitons and there place the aforementioned two leaves of the bow, each on one side, their wide end on the strip of wood fixed to the side of the intermediate cross-member into the notch that has been set aside, and two hooks of green oak are placed at the side of each end and firmly nailed, intended to prevent it sliding out of its location. Each leaf exactly faces the other, so that the two have the air of having been made as one; the curved portion of the two leaves should each be placed on the side cross-member which it is near; the string (watar) should be placed in the notches in the two curves as usual; the duct (majrât) is placed in the middle opposite, so that the string (watar) is fitted to the crank, which we will discuss in its place, if God is willing.

Finally, the pitons are removed (is the "net" then removed also?) and the giant composite bow is installed.

Whatever is going on here, it is certainly not a torsion catapult (imho).

[Urselius]

The obvious problem with interpreting the description as simply a giant crossbow is that it does not account for the presence of the horsehair and silk "nets". That is quite a large elephant to be in the room.

"Then the net (ziyâr) in question is wound around pitons of boxwood to the other one, on both sides, until it is well stretched; these pitons must be big for when the torsion around them reached its maximum; and that [ illegible Arabic words ] their location has the width of the leaf of the bow when it is in place."
"And then we remove (?) these pitons and there place the aforementioned two leaves of the bow, "

This looks a lot like the "pitons" are formers used for an initial winding of a torsion skein, which are then are replaced by the bow arms themselves.

The fact that the bow arms are of composite construction like those of hand bows may merely reflect that the stresses acting on them are such that a simple piece of wood could not be used.

[D B Campbell]

The obvious problem with interpreting the description as simply a giant crossbow is that it does not account for the presence of the horsehair and silk "nets". That is quite a large elephant to be in the room.

The obvious problem, in my opinion, is that the passage reads like someone describing a machine that they don't understand. We encounter a similar problem with Ammianus Marcellinus. Thankfully, Heron and Philon seem to understand the machines that they are describing.

I can see why David Nicolle would like the machine to be a torsion catapult. (Actually, I would like to have an Islamic scholar explain what the word ziyâr actually means. And what word the French translator has translated as "torsion".) But Nicolle's reconstruction has added so many elements that are not in the description that I wonder how accurate it can possibly be.

The fact that the bow arms are of composite construction like those of hand bows may merely reflect that the stresses acting on them are such that a simple piece of wood could not be used.

Bendy arms are counter-productive to torsion springs. You need an inflexible arm in order to twist the spring and store energy there.