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The scorpio or scorpion was a type of Roman artillery piece. Also known by the name of the triggerfish, it was described in detail by Vitruvius. In the progressive evolution of catapults, the next major improvement after the scorpio was the cheiroballistra.
The scorpio was a smaller catapult-type weapon, more of a sniper weapon than a siege engine, operated by one man. The scorpio was basically an early crossbow, a "catapult with bolts", probably first invented by the Greeks, then later adopted and used on a larger scale by the Roman legions. This catapult used a system of torsion springs to propel the bolts.
The complexity of construction and in particular the torsion springs (which the Romans referred to as tormenta) led to great sensitivity to any variation in temperature or moisture, which limited their use. Moreover, this type of technology, which disappeared by the High Middle Ages (with the exception of the Byzantine Empire which was the continuation of the Roman Empire in the Middle Ages), reappeared during the First Crusade in the form of a new type of catapult based on a system of slings and counterweights for the projection of stone balls, and as giant crossbows as the field of metallurgy progressed.
During the Roman Republic and early empire, sixty scorpions per legion was the standard, or one for every centuria. The scorpio had mainly two functions in a legion. In precision shooting, it was a weapon of marksmanship capable of cutting down any foe within a distance of 100 meters. During the siege of Avaricum in the war against the Gauls, Julius Caesar describes the terrifying precision of the scorpio. In parabolic shooting, the range is greater, with distances up to 400 meters, and the firing rate is higher (3 to 4 shots per minute). With precision shooting the rate of fire was significantly less.
Scorpions were typically used in an artillery battery at the top of a hill or other high ground, the side of which was protected by the main body of the legion. In this case, there are sixty scorpions present which can fire up to 240 bolts per minute at the enemy army. The weight and speed of a bolt was sufficient to pierce enemy shields, usually also wounding the enemy so struck.
The Scorpion was often a cumbersome and costly siege weapon , as it was quite difficult to move and acted as a more fixed weapon used for long-range defense.