This article describes a Roman-style crossbow or ''arcuballista'' with a simple nut and trigger lock. Not much is known about these weapons due to lack of sources (see Baatz 1999: 14-16; Harmuth 1986: 20-22). This crossbow is an effort to make something similar to what Romans used. However, the bow itself is made from wood and is not of composite construction: this is where the crossbow differs most from the Roman counterparts we are aware of.
The full CAD drawings are available here:
If you have any questions, please send mail to my Google mail account (samuli.seppanen).