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ROMAN ARTILLERY
Fig. SL008 The carroballista, the Roman army's mobile artillery piece from Trajan's Column.
Andrew Brozyna
Posted in 2005
To supplement their forces, the Romans used various forms of artillery. These were based on those originally developed by the Greeks. Vitruvius, one of Julius Caesar's doctores
ballistarum (artillery experts), wrote on the subject around 25BC. These were torsion machines, meaning they were powered by twisted cords. When triggered, a considerable amount of energy was released and directed toward launching the projectile. There were two types: stone and arrow (bolt) firing. Unfortunately, the Latin terms used to describe the different types of siege machines are not fully understood. In the 2nd century AD the term, ballistae, was applied to both arrow throwing and stone throwers. In the 4th century AD it appears that the arrow throwing machines were differentiated from stone throwing catapults by having the term ballistae apply only to them.
Both types of artillery were manned by men called ballistarii. It is not known exactly how many each legion had. Each cohort may have had only 1, or as many as 6. Auxiliary units did not have artillery. If these foreigners should turn against the legions, the Romans did not want them to have the added firepower of artillery. In the 2nd century AD the carroballista was introduced. See above illustration. It improved upon the static arrow-shooting device by mounting it on a type of cart. By the 4th century AD the legions no longer had a compliment of artillery. Artillery was reserved, instead, for a few specialist artillery legions and for defending fixed positions. Artillery was also used on warships. They were often mounted on wooden towers, giving them a more advantageous angle of fire.
The Onager was named after a wild ass because of the way it kicked back upon firing. It was first mentioned in writing in the 200s BC. It was most common in the armies in the mid 4th century AD. Since they were so large and slow to move the onagri were most suited for sieges. The length of the sling on the end of the arm could be adjusted to affect the trajectory of the stone.
The balisata pictured here is a scorpio (circa 50BC). It threw a bolt 27 inches long (67cm). Quite a few of these bolts survived till today. Obviously, it would have been impossible to find feathers large enough to provide stability to these over-sized arrows, so the flights were made of leather or wood. The iron points were pyramid shaped. The hand cranks at the rear were used to winch the arrow, or bolt, back to the firing position. The photo is courtesy of the R.M.R.S.