The early history of the crossbow

[Thomas V.]

Finally, third, all the finds of the three nuts (Buiston Crannog, Southgrove Farm and Carnuntum) and the bone handle (Southgrove Farm), which can be conditionally ascribed to the Roman period, were discovered in the 19th century. Unfortunately, the context and the circumstances of those finds are not entirely clear (even in the case of Max von Groller), and they actually might turn out to belong to the Medieval period. And the handle from Southgrove Farm does not necessarily belong to a crossbow. For example, in the original article of 1894 it was presented as a knife handle.

This article features the three aforementioned nuts (if anybody should be interested): http://ads.ahds.ac.uk/catalogue/adsdata/...17_321.pdf.

[...]showing a shaped handle at the rear (for which there is really no obvious function) [...].

I disagree. If you equiped the arcuballista with an conventional twice bent trigger (like shown by my first drawing), the handle protruding from the rear end would serve as a thumb rest and thus as a counterfort everytime the other four fingers push the trigger up.