Weird little Late Roman Crossbow / Arcuballista

[Dane]

Hi all. This is a fun project I just completed, a interpretation of a late-Roman crossbow. The only evidence that the Romans (this is late period, 3rd and 4th century AD) used crossbows are two grave reliefs from Gaul (France), and a few hard to interpret comments by later Roman writers. It seems that some elite horse units may have trained and used crossbows on horseback, and possibly they were used in hunting.



It is about the strangest little crossbow you can imagine. The image I am posting shows the weapon from the top down, so you can see a bolt groove and a rolling nut. The handle is particularly strange, so it is doubtful these would have been fired by bracing the stock on the shoulder, as was typical of medieval weapons. And, keeping in mind that they would have been used (possible) on horseback, there had to be means of cocking them that didn't depend on a foot stirrup. Notice no stirrup in the grave image.

I build this using some scrape red oak I had for the stock or tiller, and laminated some lignum vitae to the top surface. The handle I turned on my wood lathe out of some nice cocobolo, and the binding block is made from olive wood. It is certain that the original Roman weapons would have had a composite bow / tiller, but I used a spring steel bow I had on hand. It is a very, very low powered bow and rates 65# pull. The good thing about this is it is easy to span, so much so I can just rest the end of the handle against my stomach and pull back. Also, it is easy to span by placing my feet on the prod on both sides of the stock and pulling up to span. If this was composite construction, that would not be a good idea, particularly since Roman soldiers used hobnails in their boots (the hobnails were actually one of the chief ways to differential soldiers from civilians in the Roman world), and that would probably damage the prod.

I do plan to build a few more of these with higher power prods, to see what they can do. This prod is a bit on the wimpy side, so the penetration is not so great on targets, but is a lot of fun to shoot. In made up some new bolts for this little guy using pre-cut feathers and 125 grain tips from Three Rivers. The tickler / trigger is made of brass bar stock, and the rolling nut is made from moose antler bound into the tiller with brass wire, and with a hardened steel sear. The prod is bound into the stock with hemp rope which I then coated with hide glue.

Since this is such a low powered weapon, I figured brass would be fine for the tickler, but at higher power, the trigger would wear too fast, so steel would be the best option.

To shoot this, I place the handle end lightly on my cheek and sight down the bolt, using the tip of the bolt as my front sight. It actually felt natural after I got used to it, and it was pretty easy to get a feel for where this weapon shoots. I kept the distance close, 10 to 20 yards, as it isn't that hard hitting, but more powerful version of this should let me shoot at greater distances.

Dimensions are 19 1/2" long for the tiller / stock, 6 1/4 long by about 1.5" diameter handle for overall length of around 26." The prod is 32" strung nock to nock, and the string is 50- strands of B-50. Serving could be neater, too. The finish is a few coats of true oil. I was finishing this during Tropical Storm Andrea, with extremely high humidity, so the oil finish didn't dry well, but the matt look is kind of nice.

Dane

[ohma2]

thats nice work and a lot of it sir.ive made a couple all wood ones my self and they are alot off fun to build, i consider all primitive archery interesting and worth pursuing. thanks for showing it.

[dbb]

Cool!
Nice workmanship as usual.
Too bad i cant risk make one,in sweden you need a licence to have a crossbow.
So the moment i put it together im a criminal 

[PatM]

You're bleeding off most of the power in string friction. I'm not sure why people make crossbows with the prod set so low on the tiller and the string riding on the track all the way through the power stroke? If you scooped out the center of the track so that the bolt is supported at the front and back and the string rides free of obstruction on the power stroke performance will be radically improved.

[Dane]

Thanks for the encouraging words there, PatM, lol. So you are suggesting that me and every other crossbow maker back thousands of years is wrong I strongly suspect they would have come up with a scheme like yours a long time ago if it would work. And modern manufacturers like Horton and PSE are also really wrong, too. Maybe they just didn't put on their thinking caps?

If you think that solution will work, I strongly suggest that you build one and test it. I suspect you are incorrect in your assumptions, but making a prototype will settle that, certainly. It would also revolutionize the weapon.

Consider why the prod is place in it's socket in the first place. The forces are tremendous, and it gets progressively more strained as you raise the power of the prod. The heavier weapons had a steel or iron bolt riveted through the tiller just in front of the socket to prevent the stock from splitting, and that alone tells me you have some massive forces at work.

On moving up the prod to lessen string angle, pretend that your prod socket was placed so you only have, say, 1/8" or so between the prod and the top of the weapon so you have very minimal string angle, it would most likely sheer off like a sardine can lid. No such think as a shoot through the center prod, as well, and the prod has to be place at an angle relative to the nut placement to avoid massive torque to the prod.

On some medieval designs, the front is sloped down and you have a bolt rest that replaces the bolt groove, so there is less friction on the bolt as it leaves the crossbow, but the string angle due to prod placement is still the same. I use about a 6 degree angle to have the string end up so it centers on the bolt ends.

ddb, thanks. I appreciate it. On that law, that is too bad. Perhaps you can get a license or change the laws? And thanks, ohma2. They are so much fun, I agree. I have to build an all wooden one someday. The Skane bow (from Sweden, ironically) is so cool, and that is what most people base all wooden ones on.

[Dane]

By the way, PatM, I want to amend my comments a bit. I just remembered an illustration on Page 70 of Ralph Payne-Gallwey's The Book of the Crossbow (Dover edition), that describes your scoop idea, if in fact you are thinking along the same lines as Payne-Gallwey was. One of the problems with him is that he tended to go on little flights of fancy, so a lot of what you writes about can't be taken literally unless they are backed up by historical facts, such as actual artifacts. But maybe that was done as you suggested?

There is a good reason that a lot of crossbow top surfaces were inlaid with bone, and that was to minimize friction, and modern crossbows use special lubricating fluids for the same purpose, plus to help in slowing down the rate of string wear.

And finally, since that little Roman weapon I build is based on history, and the grave image has a bolt, why in the world would I not want a bolt groove with it's associated issues? Kind of like improving on a replica, only now it isn't a replica anymore

Dane

[half eye]

Mr. Dane, outstanding as usual. And in the way of an idea compliment, at first look it's sort of like the Colt Walker Dragoon to more modern cavalry......not an insult at all just shows that cavalry is/was lookin for a little more shock and awe since the first dude crawled up on a horse. Very cool indeed.
rich

[Dane]

Thank you sir. I agree with your suggestion. The Patersons that Walker's men used in that firefight led to the Walker and then the Dragoon. If in fact this crossbow was used in battle, a volley of bolts followed by drawn spathas would ruin anyone's day.

Dane

[PatM]

Not criticizing your workmanship but any crossbow with such massive friction is a very poor design. Believe me I've tested the difference, particularly with lightweight prods and it is eye-opening how much power is bled off.  It would have been less noticeable in a medieval crossbow with a 1000 pound pull and a 6 inch power stroke but that doesn't mean it's still a good or necessary idea.
 There are ways around the drawbacks you list in the sheer forces etc.
 Nobody would shoot a hand held bow and let the string rub their arm from armpit to wrist and expect top performance.
 The sheer capability of a dense grained wood is well up to the sheer forces of  holding the prod from sheering off the portion holding it in place..
 No question that a replica should have all the authentic drawbacks of the original design but that doesn't mean that it is the pinnacle of performance.
 No doubt crossbows are constantly improving but if a frictionless design hasn't been designed yet apart from the models I have made, I'm just not that interested enough in the idea to pursue it.
 A crossbow is really no different than a conventional bow in a shooting machine. I don't think they test bows with the string rubbing on anything.

[Dane]

I didn't think you were criticizing the work per se, but in the end, if the late Romans did it this way, then so will I. I really don't care about high-performing crossbows in the first place. I'd just burn my wooden crossbows and stick to modern machines if that were the case.

You may want to look at stone bows if you want frictionless bows. No chance in the world I am going anywhere near those things, though, considering what can happen if the stone flies back at your face, that can happen. I have no idea if you can covert such a bow to shoot bolts, though.

[M. Demetrius]

Would you mind showing a diagram of how your rolling nut and trigger works?

[fiddler49]

PatM is correct about the string drag. I've built a 600 lb cross bow and made a special effort at not having the string drag on the stock. Ralph Pain Galways book "The Cross Bow" has a number of errors that I found after
building my bow. I don't think he actually built them but one of his handy men did the actual work. The metal prods on many bows were non symetrical up sweeping limbs, plus they tilted the prod up a few degrees to keep string off track. Because of the very short power stroke most hunting cross bows had to be much heavier draw weight to get the same energy out of them that a self bow would have. My 600 lb cross bow is a hunting weight bow.   cheers fiddler49

[Joec123able]

Very cool I especially love the lignum vitae you put on it looks gorgeous

[loefflerchuck]

Bravo for your attempt to revive this technology.