A powerful weapon in the art of siege warfare is the ballista. “a ballista is generally taken to be a large catapult, like a crossbow, that shoots huge bolts, with force created by a winch” (Rogers, p. 267) but it is more than just that. The earliest form of the ballista was developed by the Greeks in its earliest design as a non-torsion powered weapon and became a more powerful torsion powered machine as time progressed. It went through many improvemments and adjustments to become the formidable siege weapon that they are know for. They were effectively in use by both attackers and defenders up through the middle ages until the invention of the trebuchet and the later development of the cannon, at which point the use of ballistas declined. They varied in purpose, size, design, portablility, and projectiles they fired, as well as name. That being said, the ballista made a difference in siege warfare whatever its size, shape, or if it was throwing arrows or stones.
The earliest ballistas were developed by the Greeks and were non-torsion powered. The earliest form of this kind of ballista was the gastraphetes or “belly bow” in Greek. “It was little more than a large, powerful, and flexible bow (DeVries, p. 117).” It had the look of a primitive crossbow but it did not have a footloop near the bow part of the crossbow that a person stepped in to draw the string back to fire. The gastraphetes had a concave that a person leaned on and, after placing the front of it on the ground, was able to draw the string back and “dishcarge the missile with much greater power than the traditional hand-drawn bowstring (Devries, p. 118).” It had greater range and more importantly greater power and force to help penetrate armor of enemy soldiers. A major limit to the gastraphetes was the limited power it could shoot with. It mostly shot bolts because they were lighter than stone, but bolts were only good for so much. they were great for piercing armor. They were not good to break down buildings. These non-torsion powered machines lasted for roughly 150 years, until they resurfaced during the Middle Ages and the development of the crossbow (Nossov, p. 136).
Adaptations like winches and bases brought greater power, size, stability to the gastraphetes (Devries, p. 118) but it was still limited on it’s power and size because it was non-torsion powered. The only way to increase the power and size was to change how the machine was designed. The bow springs gave way to two arms in tightly twisted springs known as torsion springs, which increased the power of the ballista a great deal. It was the change to torsion springs that gave the bolt shooting machine the label catapult, or shield breaker (Nossov, p. 136) because of how much additional power was aquired from the torsion springs. The rest of the of design stayed very similar. The other major change in design was a deeper groove that made it possible to shoot stone balls as well as the traditional bolts. This allowed for these early ballistas to be used for more impact oriented purposes like breaking walls or different fortification structures.
The power of these torsion-powered siege machines was incredible. Procopius gave an account of the incredible force with which the bolts were projected from these ballistas when he wrote about the defense of Rome in 537-38 BCE:
“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 he body of the man sank more than half its length into a tree, and pinning him to the sport where it entered the tree, it suspended him there a corpse.” (Devries, p.121, quoting Barton C. Hacker)
These engines of war were used both by attackers and defenders. For those that were attacking, they would often put the ballistas in their siege towers and use them to provide cover as they drew close to the castle or city walls (Sacks, p. 364). Those on the defensive side of the siege would mount their ballistas on platforms on their towers and shoot down on their enemies (Lawrence, p. 106). This defensive strategy may have been the circumstance in which the person Procopius wrote about died.
As time progressed, these torsion powered machines grew larger and their projectiles grew proportionally as well. The Romans made changes in the materials used to build the variety of different arrow-firing and stone-throwing ballistas, using metal parts where they could to increase the strength and life of these war machines. Changes were made to increase their portability (DeVries, p. 120). As the technology improved, so did the ballistas. As the ballistas improved, they became more common in armies and fear of these machines grew as well. Below is an example of a horse-drawn ballista. This is but one example of the different kinds of ballistas that developed since the Greek gastraphetes.
Print shows two soldiers with a horse-drawn ballista. The device, mounted on a wagon, is manipulated like a crossbow, shooting large arrows at enemy fortifications. The horses are well covered with armor. Taken from the collection Notitia utraque cum orientis tum occidentis ultra Arcadii Honoriique Caesarum tempora (1552) edited by Sigismund Gelenius (1477–1554). This part is from the De Rebus Bellicis, which contains many illustrations of weapons and engines of war.
print: engraving Source: Wikimedia Commons
There is no doubt that the ballista made a significant impact on warfare. From it’s earliest use by the Greeks, to it’s final display during the Middle Ages as the age of gunpowder set in, the ballista in all it’s varieties was an asset for siege warfare, for the defender and the attacker alike.
Works Cited
“Ballista.” Wikipedia. Wikimedia Foundation, 21 Apr. 2014. Web. 25 Apr. 2014.
DeVries, Kelly, and Robert D. Smith. “Non-gunpowder Artillery.” Medieval Military Technology. 2nd ed. Toronto: U of Toronto, 2012. 117-22. Print.
Lawrence, A. W. “Archimedes and the Design of Euryalus Fort.” The Journal of Hellenic Studies 66 (1946): 99-107. JSTOR. Web. 24 Apr. 2014.
Murray, Oswyn, and Margaret Bunson. “Warfare, Siege.” Encyclopedia of the Ancient Greek World. By David Sacks. Revised ed. New York: Facts on File, 2005. 364-65. Print.
Nicholson, Helen J. Medieval Warfare: Theory and Practice of War in Europe, 300-1500. Houndmills, Basingstoke, Hampshire: Palgrave Macmillan, 2004. 94. Print.
Nossov, Konstantin. “Ancient and Medieval Throwing Machines.” Ancient and Medieval Siege Weapons: A Fully Illustrated Guide to Seige Weapons and Tactics. Guilford: Lyons, 2006. 133-162+. Print.
Rogers, Clifford J., William Caferro, and Shelley Reid. The Oxford Encyclopedia of Medieval Warfare and Military Technology. New York: Oxford UP
Legio I Lynx Fulminata 
Actually the Gastrophetes did not use your arms or legs to pull back the string, They used a beam (diostra) sliding in a track (syrinx) with a pawl on each side of the diostra to engage hooks or ratchets (triangular teeth probably) along the edges of the syrinx, To draw the bow you extended the diostra until a double claw on the shooter’s end it engaged the string and both held the string and acted as a sear, then leaned against the belly yoke on the operator end to push the diostra in, and the sliding diostra pulled back the bow string, The pawls engaged the teeth in the syrinx as it was run back so if you slipped it wouldn’t kick your teeth in or worse. When the string was far enough back to be fired, the bolt (arrow thingy) was then put onto the track and nocked on the bow string between the claws holding the string. To fire the bolt, the tail of the claw holding the string and bolt was pushed down, the string was released, bolt was fired, and you got to do the whole thing again.
From reading a translation of Hero, it appears that the models he was talking about could also be fired from half-cock as well if it was called for because the claw holding the bow string was mounted on the diostra not on the stock or syrinx like you would expect from modern crossbows.
Have you considered building one? I think PVC would work fine for a low power mock up.
Thank you for the information. from the sources I had looked at, it wasn’t the most clear. Your explanation helps. I’ve not considered trying to build one, but it is a good idea. If I have time this summer I’ll see what I can do to put it together. Thanks again!!
So I apologize for the picture not showing up. It doesn’t show up on my computer at least so I’m assuming it’s not showing up on anyone else’s computer. If you click on the picture link it will display what I wanted to show. Again, My apologies.