Greek and Roman artillery

Main information about ancient artillery comes from the five surviving Greek and Roman sources: two treatises by Heron of Alexandria, Belopoeika and Cheiroballistra, and from the books by Biton of Pergamon, Philo of Byzantium and Vitruvius Ancient artillery consisted of elasticity-driven devices for shooting projectiles (arrows, bolts, stones etc.) which evolved from the composite bow.

The earliest artillery pieces, like gastraphetes, were driven by a composite bow. According to Marsden's analysis of ancient sources, they were invented in Syracuse in 399 BC, when tyrant Dionysius I gathered there an assembly of expert craftsmen to conduct a research on new armament. XVI.41.1-3. . Diodorus says that these were the first catapults, and describes the impression new weapons made during the siege of Motya by Dionisius. These catapults were arrow shooting and it is conjectured that they were powered by a composite bow.

More powerful pieces were driven by torsion of a spring made of an appropriate organic material, usually sinew or hair, human or horse. Torsion-powered pieces were probably invented in Macedonia, shortly before the times of Alexander III. According to Philo, Ctesibius experimented with metal springs and pneumatically powered machines, but there is no record of their actual use, because metal springs were not sufficiently resilient at that time. In the Middle Age, metal springs were successively used in crossbows.

The stone-throwing machines were torsion-powered, and their first recorded use is in the siege of Tyre by Alexander.

Torsion artillery reached its highest development in the Hellenistic period, probably at the time of Demetrius Polyorcetes. No improvement, except in details, was ever made upon the catapults of Demetrius. The Romans obtained their knowledge from the Greeks, and employed the Greek specialists. Torsion artillery was used until after the spread of gunpowder.

Nomenclature
The names of the artillery pieces changed with time. Though all inventions in the field of artillery were made by the Greeks, the best known are the Latin names, ballista and catapulta. Catapulta (καταπέλτης ὀξυβελής) originally meant an arrow- or bolt- throwing engine. A ballista (καταπελτης λιτοβολος or πετροβολος) was a more powerful machine primarily designed for throwing stones. Sometimes ballistae were used to fire extraordinary projectiles, like pots with snakes, or even parts of dead bodies, with the purpose of terrifying the enemy. For example, the Romans catapulted to the camp of Hannibal the head of his brother Hasdrubal. Artillery was also used as flame carriers. During the last night of Demetrius attack on Rhodes the Rhodians fired 800 cylinders with some incendiary substance; the cylinders being subsequently collected and counted; they managed to set fire on Demetrius' armored tower.

At some time between 100 CE and 300 CE a change occurred in the nomenclature. Thus in the 4th century CE catapulta indicates a one-armed stone-throwing engine, also known as onager, while ballista means a two-armed piece which shoots bolts only.

The authors of Greek treatises classified artillery pieces into two categories: euthytones and palintones. Hero writes that eutitones were arrow-throwing, while palintones usually stone throwing, but sometimes could also shoot arrows or both. The precise meaning of these terms is disputed. According to Schramm, Marden and their followers, this distinction reflects the difference in the shape of the detail of the frame which is called "hole carrier". According to the so-called "French school", the arms of a eurhytone extended outside the frame, while the arms of a palintone moved inside the frame. The problem arises because the ancient descriptions that we have do not contain original pictures, and the meaning of certain technical terms is unclear.

Dimensions, materials and performance
Much research was done by Hellenistic Greek scientists and craftsmen on the design of artillery pieces. The main parameter that determines the sizes of all parts of the machine is the weight of the projectile or the length of the bolt (arrow). The fundamental size characteristic is called the hole diameter; it is the same as the diameter of the spring (which is a bunch of sinew rope). Vitruvius gives the following formulas for the hole diameter: it is the length of the bolt divided by 9 for the bolt-throwing machines, or
 * $$ 1.1 (100W)^{1/3},$$

for the stone-throwing machines, where W is the weight of the projectile in Attic minas (1 mina=436.6 g), and the hole diameter is measured in dactyls (1 dactyl=19.3 mm). Then the dimensions of all parts are defined as fixed multiples of the hole diameter, for example the length of the arm is 7 hole diameters.

Most of the frame detail were made in the Hellenistic period of wood. Hero of Alexandria proposed metal frame and metal cylinders to enclose the springs. Depictions on Trajan's column and archeological evidence indicate that these metal artillery pieces were widely used by the Romans.

An important detail, washer used in the stretching of the spring was always made of metal, and these washers are the only pieces of Hellenistic artillery, besides the stone balls and arrowheads which are found by archeologists.

The preferred material for the springs was sinew and human hair. Horse hair was considered an inferior substitute. In 250 BC, Rhodes sent to Sinope for her war with Mitridates about 3/4 of a ton of women's hair. In 225 BC Seleucus gave Rhodes a present of hair weighting 1000 talents. This gift was a part of international relief program after a catastrophic earthquake. This shows that a large trade in human hair existed in Hellenistic period.

A typical ballista could throw a stone weighting 1 talent (60 minae = 26.2 kg) at the distance of 400 yards. There existed heavy ballistae able to throw stones weighting 3 talents and more.

Much longer ranges were claimed by Athenaeus Mechanicus ''...a three-span catapult shot 700 yards (three and half stades); its springs weighted twelve minae. A four-cubit palintone engine shot 800 yards (four stades)''.

Athenaeus mentions a catapulte designed by Archimedes which could throw a three talent stone at the distance of one stade. This catapult was installed on a ship. Polybius (VIII,7,9) writes that catapults used to defend Syracuse during the siege by Marcellus were throwing stones of 10 talents (262 kg). The largest weight of projectiles mentioned in Vitruvius is 460 pounds.

When describing the siege of Jerusalem by Titus, Josephus writes that ''the stone balls that were being hurled weighted one talent and traveled two or more stades (400 yards)''.

Philo of Byzantium writes that the stone walls have to be at least 10 cubits (about 3 meters) thick to be unaffected by stone-shot.

According to Schramm, the best arrow-throwing catapults could be trusted to kill a man at 100 yards, so the accuracy was better than of an early 19th century musket.

Use
The main use of artillery was in the siege of fortified places. The heavy stone-throwing pieces were used to destroy the walls, while the lighter arrow-shooting pieces to clear the walls from the enemy defending them

Several attempts to use artillery in the field are recorded but they were mostly unsuccessful, except when the artillery could be deployed in some protected place. For example, in the Battle of Jaxartes Alexander used catapults to clear the further bank of the river.

The artillery pieces were transported in disassembled state, and it took long time to assemble, install and adjust them. In many cases only few essential parts of artillery pieces were transported, the rest could be made on the place of a siege if timber was available.

Artillery was used in naval battles, as mentioned in Diodorus, book XX. Both Alexander and Demetrius mounted catapults on ships for the purpose of attacking fortresses.

Testing modern replicas
Many attempts were made in modern times to reproduce the ancient artillery pieces, following their ancient descriptions, and to test them. The first success was due to German general E. Schramm in collaboration with A. Rehm. They used horse hair for the springs, and achieved the distance of over 300 m with 1 pound lead shot, and using another machine, 370 meters with 1 meter bolt. This bolt penetrated an iron-plated shield 3 cm thick to half of the bolts length.

Nowadays many working replicas of various types exist.