Our new cheiroballista...

[John Conyard]

I've just come across the thread. It's very good to see such a beautiful machine. Congratulations. I've even checked the garage to make such ours is still there

I fear I'm not the best person to comment on Roman artillery. I lost interest when I realised I couldn't mount it on the front of my saddle. However I have had to repair our machine a few times and know it quite well. Our's arrived in 2006, and it's called "Constantine".

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It shoots an 85g bolt around 210m, which I would suggest is half the distance of a 4th century machine. James raised the possibility that at Dura different sizes of bolt could have been deliberately used, the finds naturally falling into bands of 290-300mm, 330mm, 350-365mm, 385-400mm and 430-435mm long, from the tip of the tail to the beginning of the iron socket. This seems very likely. It would mean that using a ballista at constant power, varying distances could be achieved by using bolts of differing lengths. For maximum distance the Comitatus ballista shoots bolts with a shaft of 190mm. A shaft length of 400mm reduces the range on average by 20m. But the greater weight of the longer bolt of 100g insures greater penetration of the target. In effect the operator of the ballista could select different bolts for different tasks.

I do enjoy using birch from my local wood to make bolts of various sizes. Our blacksmith makes the heads. Indeed, it was almost a year ago whilst watching semi-drunk legionaries trying to repair bolts in the dark with very sharp blades, that I first became interested to constructing the bolts and attaching the flights. I have a 400mm bolt taped to a large rocket with a blank .22 shell under the iron head. I suspect it will not work, but the theory is you light the blue touch paper, shoot the bolt from the ballista, watch the rocket kick in, hit something, and the shell shoots the head into the target. The length of the rockets tail is very important. It's a dream.

We generally use the machine at full or very near full tension. After two years the copper alloy claw sheared. We now use steel. Last year the winch rope broke. I tried using climbing rope stressed to just over 800lb, but it broke before we reached full tension. We change the arms regularly just in case. In fact I carry spare parts to every show.Despite the semi-humorous tone of this message, safety is always the prime concern. It pays to have an experienced member standing back just watching what the crew are doing. Just in case.