Carroballista

According to the Roman author Vegetius (Epitoma rei militaris II.25), each legion had 55 carroballistae (one per centuria) which were arrow/bolt-shooter of the cheiroballistra (Greek: χειροβαλλίστρα) type.

The structure of the carroballista machine is identical to that of the cheiroballistra or manuballista, which translates in all its forms to "hand ballista", was an imperial-era Roman siege engine.

In fact, the light but stout metal spring-frame and the wider space in the frontal part of the machine given by the arched strut conferred a greater manoeuvrability to the whole ballista.

But the bolts or arrows are here depicted in a ready-to-fire position, hazardous for artillerymen if the ballistae are simply being transported in order to be dismounted and deployed on the battlefield.

There are many hypotheses about the structure of the cart and probably different models of the same machine seem to have been in use at the same time: Many scholars do not have an opinion about this problem, due to scarce evidence, as clearly stated by Alan Wilkins.