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The ballista (Latin, from Greek βαλλίστρα – ballistra and that from – βάλλω ballō, "throw"), plural ballistae, was an ancient missile weapon that launched a large projectile at a distant target.
Developed from earlier Greek weapons, it relied upon different mechanics, using two levers with torsion springs instead of a prod, the springs consisting of several loops of twisted skeins. Early versions projected heavy darts or spherical stone projectiles of various sizes for siege warfare. It developed into a smaller sniper weapon, the scorpio, and possibly the polybolos.
Greek weapon 
The early ballista in Ancient Rome was developed from two weapons called oxybeles and gastraphetes. The gastraphetes ('belly-bow') was a hand held crossbow. It had a composite prod and was spanned by bracing the front end of the weapon against the ground while placing the end of a slider mechanism against the stomach. The operator would then walk forward to arm the weapon while a ratchet prevented it from shooting during loading. This produced a weapon which, it was claimed, could be operated by a person of average strength but which had a power that allowed it to be successfully used against armoured troops. The oxybeles was a bigger and heavier construction employing a winch, and was mounted on a tripod. It had a lower rate of fire and was used as a siege engine. With the invention of torsion spring bundle technology, the first ballista was built. The advantage of this new technology was the fast relaxation time of this system. Thus it was possible to shoot lighter projectiles with higher velocities over a longer distance.
For an oxybeles, the rules of a torsion weapon demanded that the more energy could be stored, the thicker the prod had to be and the heavier the projectile, to increase the amount of stored energy delivered to the projectile. The earliest form of the ballista is thought to have been developed for Dionysius of Syracuse, circa 400 BC.
The Greek ballista was a siege weapon. All components that were not made of wood were transported in the baggage train. It would be assembled with local wood, if necessary. Some were positioned inside large, armoured, mobile siege towers or even on the edge of a battlefield. For all the tactical advantages offered, it was only under Philip II of Macedon and even more so under his son Alexander, that the ballista began to develop and gain recognition as both siege engine and field artillery. Polybius reports about the usage of smaller more portable ballistae, called scorpions, during the Second Punic War.
Since these weapons delivered lighter munitions (thus delivering less energy on impact) it is a widely held opinion that they were used more as an anti-personnel role, or to destroy lighter structures. A less accurate weapon like an onager or other single-arm artillery could hit with more force, and thus would be the more useful weapon against reinforced wood or heavy masonry.
Ballistae could be easily modified to shoot both spherical and shaft projectiles, allowing their crews to adapt easily to prevailing battlefield situations in real time.
As the role of battlefield artillery became more sophisticated, a universal joint (which was invented just for this function) was integrated into the ballista's stand, allowing the operators to alter the trajectory and firing direction of the ballista as required without a lengthy disassembly of the machine.
Roman weapon 
After the absorption of the Ancient Greek city-states into the Roman Republic in 146 BC, the highly advanced Greek technology began to spread across many areas of Roman influence. This included the great military machine advances the Greeks had made (most notably by Dionysus of Syracuse), as well as all the scientific, mathematical, political and artistic developments.
The Romans 'inherited' the torsion powered Ballista, which had by now spread to several cities around the Mediterranean, all of which became Roman spoils of war, including one from Pergamum, which was depicted among a pile of 'trophy' weapons in relief on a balustrade.
The torsion ballista, developed by Alexander, was a far more complicated weapon than its predecessor and the Romans developed it even further, especially into much smaller versions, that could be easily carried.
Early Roman ballistae 
The early Roman ballistae were made of wood, and held together with iron plates around the frames and iron nails in the stand. The main stand had a slider on the top, into which were loaded the bolts or stone shot. Attached to this, at the back, was a pair of 'Winches' and a 'Claw', used to ratchet the bowstring back to the armed firing position.
The slider passed through the field frames of the weapon, in which were located the torsion springs (rope made of animal sinew), which were twisted around the bow arms, which in turn, were attached to the bowstring.
Drawing the bowstring back with the winches twisted the already taut springs, storing the energy to fire the projectiles. The bronze or iron caps, which secured the torsion-bundles were adjustable by means of pins and peripheral holes, which allowed the weapon to be tuned for symmetrical power and for changing weather conditions.
The ballista was a highly accurate weapon (there are many accounts of single soldiers being picked off by ballista operators), but some design aspects meant it could compromise its accuracy for range. The maximum range was over 500 yards (460 m), but effective combat range for many targets was far shorter. The ballista's relatively lightweight bolts also did not have the high momentum of the stones thrown by the later onagers, trebuchets, or mangonels; these could be as heavy as 200-300 pounds (90–135 kg).
The Romans continued the development of the Ballista, and it became a highly prized and valued weapon in the army of the Roman Empire.
It was used, just before the start of the Empire, by Julius Caesar during his conquest of Gaul and on both of his campaigns in subduing Britain. Both attempted invasions of Britain and the siege of Alesia are recorded in his own Commentarii (journal), The Gallic Wars (De Bello Gallico).
First invasion of Britain 
The first invasion of Britain took place in 55 BC, after a rapid and successful initial conquest of Gaul, in part as an expedition, and more practically to try to put an end to the reinforcements sent by the native Britons to fight the Romans in Gaul.
A total of eighty transports, carrying two legions, attempted to land on the British shore, only to be driven back by the many British warriors assembled along the shoreline. The ships had to unload their troops on the beach, as it was the only one suitable for many miles, yet the massed ranks of British charioteers and javeliners were making it difficult.
Seeing this, Caesar ordered the warships – which were swifter and easier to handle than the transports, and likely to impress the natives more by their unfamiliar appearance – to be removed a short distance from the others, and then be rowed hard and run ashore on the enemy’s right flank, from which position the slings, bows and artillery could be used by men on deck to drive them back. This manoeuvre was highly successful.
Scared by the strange shape of the warships, the motion of the oars, and the unfamiliar machines, the natives halted and retreated. (Caesar, The Conquest of Gaul, p99)
Siege of Alesia 
In Gaul, the stronghold of Alesia was under a Roman siege in 52 BC, and was completely surrounded by a Roman fortifications including a wooden palisade and towers. As was standard siege technique at the time, small ballistae were placed in the towers with other troops armed with bows or slings.
Ballistae in the Roman Empire 
During the days of the conquest of Empire, the ballista proved its worth many times, in sieges and battles, on sea and on land. It was even used to quell riots. It is from the time of the Roman Empire that many of the archaeological finds of ballistae date and in these times that many of authors wrote their accounts and whose technical manuals and journals are used today by archaeologists to reconstruct these weapons.
After the time of Julius Caesar, the ballista was a permanent fixture in the Roman Army and, over time, modifications and improvements were made by successive engineers. This included replacing the remaining wooden parts of the machine with metal, creating a much smaller and lighter machine, capable of even more power than the wooden version, and which required less maintenance (though the vital torsion springs were still vulnerable to the strain).
Cheiroballistra / Manuballista 
The Cheiroballistra and the Manuballista (hereafter Manuballista) are held by many archaeologists to be the same weapon. The difference in names comes from the different languages spoken in the Empire. Latin remained the official language in the Western Empire, but the Eastern Empire predominantly used Greek, which added an extra 'r' in the word Ballista.
The Manuballista was a handheld version of the traditional Ballista. This new version was made entirely of iron, which conferred greater power to the weapon, since it was smaller, and less iron (an expensive material before the 19th century), was used in its production. It was not the ancient Gastraphetes, but the Roman weapon. However, the same physical limitations applied as with the Gastraphetes.
The Carroballista was a cart-mounted version of the weapon. Probably there were different models of this cart-mounted ballista of the Cheiroballistra Class, at least 2 different models with 2 wheels and 1 model with 4 wheels. Probable size 1.47 m width, i.e. 5 Roman Feet. The cart system and structure gave it a great deal of flexibility and much more ability as a battlefield weapon, since the increased maneuverability allowed it to be moved with the flow of the battle. This weapon features several times on Trajan's Column.
According to some sources, the Roman military, at one time in its history, also fielded 'repeating' ballistae, also known as a polybolos. Reconstruction and trials of such a weapon carried out in a BBC documentary 'What the Romans Did For Us' showed that they "were able to shoot eleven bolts a minute, which is almost four times the rate at which an ordinary ballista can be operated". However, this has not yet been found archaeologically. They operate using a cam to pull the mensa (the place where the projectile travels on) backwards and the string along with it. At the rearmost position, the string is unlocked and propels the projectile forwards. The mensa is then pushed forward and pushes a bolt out of the magazine above it, and latches on to the string, all done with the rotating cam. The cycle then repeats.
Archaeology and the Roman ballista 
Archaeology, and in particular Experimental archaeology has been influential on this subject. Although several ancient authors (such as Vegetius) wrote very detailed technical treatises, providing us with all the information necessary to reconstruct the weapons, all their measurements were in their native language and therefore highly difficult to translate.
Attempts to reconstruct these ancient weapons began at the end of the 19th century, based on the rough translations of ancient authors. It was only during the 20th century, however, that many of the reconstructions began to make any sense as a weapon. By bringing in modern engineers, progress was made with the ancient systems of measurement. By redesigning the reconstructions using the new information, archaeologists in that specialty were able to recognize certain finds from Roman military sites, and identify them as ballistae. The information gained from the excavations was fed into the next generation of reconstructions and so on.
Sites across the empire have yielded information on ballistae, from Spain (the Ampurias Catapult), to Italy (the Cremona Battleshield, which proved that the weapons had decorative metal plates to shield the operators), to Iraq (the Hatra Machine) and even Scotland (Burnswark siege tactics training camp), and many other sites between.
The most influential archaeologists in this area have been Peter Connolley and Eric Marsden, who have not only written extensively on the subject but have also made many reconstructions themselves and have refined the designs over many years of work.
Middle Ages 
With the decline of the Roman Empire, resources to build and maintain these complex machines became very scarce, so the ballista was supplanted initially by the simpler and cheaper onager and the more efficient springald.
Though the weapon continued to be used in the Middle Ages, it faded from popular use with the advent of the trebuchet and mangonel in siege warfare. The crossbow and the longbow supplanted it as a sniper weapon. They all were simpler to make, easier to maintain (no anointment) and much cheaper.
See also 
- Ballistra, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus
- Ballo, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus
- Warry, J. (1995). Warfare in the Classical World. pp 178. Salamander Books Ltd., London: United Kingdom. ISBN 0-8061-2794-5
- Discovering Roman Technology, by Adam Hart-Davis
|Reenactor with manuballista, Retrieved 6 February 2008|
|Trigger of the polybolos, retrieved 6 February 2008|
|Side elevation of the polybolos, retrieved 6 February 2008|
|From above with magazin removed, retrieved 6 February 2008|
|Another view of the trigger, retrieved 6 February 2008|
- Caesar (tr Handforth), 1982, The Conquest of Gaul, London: Penguin Books
- Campbell, D; 2003, Greek and Roman Artillery 399 BC – AD 363, Osprey
- Connolly, P; 1975, The Roman Army, Macdonald Educational
- Connolly, P; 1998, Greece and Rome at War, Greenhill Books
- Feugère, M; 2002, Weapons of the Romans, Arcadia
- Goldsworthy, A; 2003, The Complete Roman Army, Thames and Hudson
- Marsden, E.W; 1971, Greek and Roman Technical Treatises, Clarendon
- Warry, J. ;1995, Warfare in the Classical World, Salamander Books Ltd., London: United Kingdom. ISBN 0-8061-2794-5
- Wilkins, A; 2003, Roman Artillery, Shire Archaeology
|Wikimedia Commons has media related to: Ballista|
- Roman Stone Throwing Ballista
- Ancient Greek Artillery Technology
- Reconstructions and Plans of Greek and Roman Artillery[dead link]
- Plans For a Working Model Ballista
- The reconstruction of a full-size working ballista by BBC TV and the Discovery Channel