high-maintenance devices and vulnerable to having their leather, sinew, or hemp skeins affected by wet or even damp, which would cause them to slacken and lose tension, rendering the engine useless. It is somewhat difficult to clearly define and describe Roman artillery, as names are easily confused and historians still do not agree on all definitions. Perhaps best known are the ballista, the onager, and the scorpio. Ballista After the absorption of the ancient Greek city states into the Roman Republic in 146 BC, some advanced Greek technologies began to spread across many areas of Roman influence. This included the hugely advantageous military 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 ballistae which had by now spread to several cities around the Mediterranean, all of which became Roman spoils of war in time, 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. Vitruvius, in his De Architectura book X, describes the construction and tuning of ballistae. Every century (group of 60-100 men) in the Roman army had a ballista by the 1st century AD. It was the command of the chief of the ballistae, under whom were the artillery experts, or doctores ballistarum and finally, the artillerymen, or ballistarii. Ballistae were heavy missile weapons, hurling large rocks great distances to damage rampart walls. They resembled large crossbows, rather than catapults. They were powered by two horizontal like arms, which were inserted into two vertical and tightly wound "skein" springs contained in a rectangular frame structure making up the head or principal part of the weapon. The arms were drawn rearward with a winch lever to further twist the skeins and thus gain the torsion power to cast a projectile. It has been said that the whirring sound of a ballista-fired stone struck fear and dread into the hearts of those inside the walls of besieged cities. The stones chosen to be used in the ballista had to be a particular sort. According to Vegetius, river stones were best, since they are round, smooth, and dense. Ballista stones found at the site of Masada were chiseled to make them as