The late 4th century author Vegetius provides the only contemporary account of ancient Roman crossbows. In his "De Re Militaris", he describes "arcubalistarii" (crossbowmen) working together with archers and artillerymen. However it is disputed if arcuballistas were even crossbows or just more torsion powered weapons. The idea that the arcuballista was a crossbow is based on the fact that Vegetius refers to it and the "manuballista", which was torsion powered, separately. Therefore, if the arcuballista was not like the manuballista, it may have been a crossbow. The etymology is not clear and their definitions obscure. According to Vegetius, these were well-known devices, and hence he did not describe them in depth.