Crossbow
Ancient Rome

The late 4th century author Vegetius, in his De Re Militari, describes arcubalistarii (crossbowmen) working together with archers and artillerymen. However it is disputed whether arcuballistas were crossbows or torsion-powered weapons. The idea that the arcuballista was a crossbow is due to Vegetius referring separately to it and the manuballista, which was torsion powered. Therefore, if the arcuballista was not like the manuballista, it may have been a crossbow. According to Vegetius these were well-known devices and hence he did not describe them in depth. Joseph Needham argues against the existence of Roman crossbowmen:

On the textual side, there is almost nothing but passing references in the military historian Vegetius (fl. + 386) to 'manuballistae' and 'arcuballistae' which he said he must decline to describe as they were so well known. His decision was highly regrettable, as no other author of the time makes any mention of them at all. Perhaps the best supposition is that the crossbow was primarily known in late European antiquity as a hunting weapon, and received only local use in certain units of the armies of Theodosius I, with which Vegetius happened to be acquainted.

On the other hand Arrian 's earlier Ars Tactica, from about 136 AD, also mentions 'missiles shot not from a bow but from a machine' and that this machine was used on horseback while in full gallop. It is presumed that this was a crossbow.

The only pictorial evidence of Roman arcuballistas comes from sculptural reliefs in Roman Gaul depicting them in hunting scenes. These are aesthetically similar to both the Greek and Chinese crossbow but it is not clear what kind of release mechanism they used. Archaeological evidence suggests they were similar to the rolling nut mechanism of medieval Europe.
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