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My son wants to make an onager that's based on the ancient Roman ones, so I'm curious as to what kind of methods the ancient Romans would have used to attach wooden beams together.

They didn't have threaded steel nuts and bolts, did they? How did they attach wooden beams together? Nails? Fitted notches and glue? Dowels and friction? It seems like a really simple question, but it seems to me that the whole point of a kid building a small onager is to build one whose construction and operation are basically historical, as a learning exercise. Otherwise, why use an onager at all? You might as well just use PVC pipes and a bicycle pump for compressed air, so you can accurately aim the damned thing.

I can’t say anything on Roman catapults specifically, but mortise and tenon joints held by internal or external pins is the standard means of joining beams without metal plates and fasteners. It’s been used for all manner of woodworking since before Roman times, it’s very strong and it makes for quick assembly and disassembly. Once the pins are removed everything can just be knocked apart with hammers. Glue be used to hold the pins in for good.

Asked some friends who built one but they said they didn't know about any archeological evidence for what materials where used to attach the beams. But they did send me this link:
http://www.algobeautytreb.com/
I hope it might be of some interest.

Most of the joints were good old carpentry joints, and secured by dowels, and in case of bigger constructions, nails and iron fittings.

Sometimes these joints got secured by rope-wrapping. Some tighter wrapping was made by wet rawhide or leather that shrank while drying. But 'ex manufactura', they had none, or metal reinforcements.

Are you going to use the 'twist a bunch of sinew' or the 'giant bow' variety for propulsion? Spoon or sling head?

Thanks for the info, guys. Looks like we'll just use notching and dowels then, which is simple enough and would have been within their capabilities.

LaCroix wrote:Sometimes these joints got secured by rope-wrapping. Some tighter wrapping was made by wet rawhide or leather that shrank while drying. But 'ex manufactura', they had none, or metal reinforcements.

I don't think we'll bother with that. Hammering in dowels should make it strong enough, especially since it's going to be small-scale.

Are you going to use the 'twist a bunch of sinew' or the 'giant bow' variety for propulsion? Spoon or sling head?

I figured we'd just use some cheap nylon rope and twist it. We want to be reasonably accurate in terms of general concept, but we also want it to be cheap and convenient. They wouldn't have had nylon rope, but the execution would be identical, and I already have some.

I know know anything about the subject, but I did search around a bit. There's a book called Roman woodworking by Roger B. Ulrich. Here's a direct link to chapter 4 which is all about joints, if that's any help.

Darth Wong wrote:]
I figured we'd just use some cheap nylon rope and twist it. We want to be reasonably accurate in terms of general concept, but we also want it to be cheap and convenient. They wouldn't have had nylon rope, but the execution would be identical, and I already have some.

I imagine that rubber tarp straps would be a closer approximation. Though, I'm not familiar with the properties of tendons.

EDIT: Also, possibly more dangerous to work with.

What kind of Onager are you building?

Thanas wrote:What kind of Onager are you building?

There are a lot of different varieties? I just figured it would look something like what we've seen in movies: a rectangular frame with a vertical section, some trusses for rigidity, a bundle of rope holding a swing arm, and some kind of mechanism for pulling the arm down and locking it into place prior to triggering a release. Did they have standardized designs at the time?

An Onager can use a sling somewhat like a Trebuchet, or they can use the classic fixed wooden bowl. That’s the only major difference in types I’ve ever heard of, other then basic issues of scale and the length of the throwing arm. Roman Legions would build new siege machines for each new campaign, so no truly standard design existed.

No one had any compelling reason to standardize artillery designs until the 1500s, when warships started mounting as many as 100 cannon and someone thought it might be nice if they didn’t need 100 different sizes of ammo. For a catapult, just chisel the stone until it’s the right size.

You might still see something close to standardization in a large military, perhaps? Not in the sense of interchangeable parts, but in the sense that you can easily categorize a given artillery piece as "X-weight catapult" or whatever? You know, so that the measurements you needed to work from in building the thing were roughly known, and so that commanders could make a reasonable estimate about how far it could throw?

Simon_Jester wrote:You might still see something close to standardization in a large military, perhaps? Not in the sense of interchangeable parts, but in the sense that you can easily categorize a given artillery piece as "X-weight catapult" or whatever? You know, so that the measurements you needed to work from in building the thing were roughly known, and so that commanders could make a reasonable estimate about how far it could throw?

This is just speculation off the top of my head, but...

The Roman army usually had quite a number of veteran troops at most points in its existence. Given that standard terms of enlistment were around twenty years or so, most veterans would have gone through a siege or two in their time. As such, I can see catapult-building being along the lines of 'umm, this is what we did six years ago at So-and-So, we built it like this...'. There may have been some standard forms, and certainly the forms of propulsion were probably standard; it's just that they didn't have a Blueprint, Trebuchet Mark IV, 'Caesar Imp.' Pattern kinda thing going on to draw from, and as such, troops that had built them before would rebuild them from memory when needed.

Granted, all this doesn't have any sources, but I'm just throwing this thought out there...

Simon_Jester wrote:You might still see something close to standardization in a large military, perhaps? Not in the sense of interchangeable parts, but in the sense that you can easily categorize a given artillery piece as "X-weight catapult" or whatever? You know, so that the measurements you needed to work from in building the thing were roughly known, and so that commanders could make a reasonable estimate about how far it could throw?

Certainly at the Legion-Army levels you could see a degree of standardization for roles and size, like they'd have a big one for smashing battlements, and a small one for throwing clusters of stones to suppress manpower. But the Romans had no compelling reason to adapt Empire wide standards like we expect a modern military too. Different availabilities of woods, different threats and the shear distances and slow pace of travel and communications would prevent standardization from having any advantages. Roman also just lasted quite a few hundred years, so you’d expect the wood working would have improved over time.

Darth Wong wrote:My son wants to make an onager that's based on the ancient Roman ones, so I'm curious as to what kind of methods the ancient Romans would have used to attach wooden beams together. They didn't have threaded steel nuts and bolts, did they? How did they attach wooden beams together? Nails? Fitted notches and glue? Dowels and friction? It seems like a really simple question, but it seems to me that the whole point of a kid building a small onager is to build one whose construction and operation are basically historical, as a learning exercise. Otherwise, why use an onager at all? You might as well just use PVC pipes and a bicycle pump for compressed air, so you can accurately aim the damned thing.

Try asking HERE These guys spend all their time talking about the detailed aspects of Roman civilian and military life. They spent five pages once discussing the shape of cheekpieces on Roman helmets.

Elheru Aran wrote:This is just speculation off the top of my head, but...

The Roman army usually had quite a number of veteran troops at most points in its existence. Given that standard terms of enlistment were around twenty years or so, most veterans would have gone through a siege or two in their time. As such, I can see catapult-building being along the lines of 'umm, this is what we did six years ago at So-and-So, we built it like this...'. There may have been some standard forms, and certainly the forms of propulsion were probably standard; it's just that they didn't have a Blueprint, Trebuchet Mark IV, 'Caesar Imp.' Pattern kinda thing going on to draw from, and as such, troops that had built them before would rebuild them from memory when needed.

Granted, all this doesn't have any sources, but I'm just throwing this thought out there...

What a lot of people forget is that the Legion was a very mobile army, with a far-spread series of forts and other supply dumps set up along well-paved roads throughout the majority of the Empire. If they were in an area with access to these supplies, an onager might be 'in storage', either broken down in easily-carted parts, or a fully assembled model that the Legion's Auxillary Corps could transport via horse or ox-train. When they reached their target, veteran Engineers would assemble the parts following their training, passing that training on to the rookies, who would possibly be assigned to the Auxilleries of the Legion for the rest of their enlistment.

The Roman Legions had a lot of surprisingly modern tricks up their sleeves.

There's actually a surprising amount of mathematics that goes into designing siege weapons. Most of these were determined through trial and error and some were actually written down into what could be considered books.
Remember the Romans got a lot of their knowledge from the Greeks who were willing to write down just about anything.
Siege engineers would have tables that they could consult for things such as how large a counter weight would be needed to throw a stone of X weight X distance.
As an aside these books of tables led to a low status of engineers in the Greek and Roman philosophical world. Because they used references and didn't model things from beginning to end that is.
And to answer the inevitable "How do you know this?" question, in the spring of 2009 I was able to take a fourth year history class in the History of technology and warfare at Simon Fraser University. We spent a few classes talking about Siege weapons in the ancient world and the implications.

You also have specialized siege troops in the roman world. Usually auxillaries, but later entire legions were formed just for the purpose of siege artillery. Undoubtedly those carried their weapons with them at all times.

As for romanarmytalk.com, I think Mike would be far better served by checking a library to see real, serious and peer-reviewed work. A good choice would be to just take any book about the roman army and just look into references and sources. I know of a few good studies, but sadly they are all in German.

Thanas wrote: As for romanarmytalk.com, I think Mike would be far better served by checking a library to see real, serious and peer-reviewed work. A good choice would be to just take any book about the roman army and just look into references and sources. I know of a few good studies, but sadly they are all in German.

True; but the forum I quoted does seem to be well-informed and they are likely to be able to give a quick answer which is the primary need here. Proper research can always follow up the quick-and-dirty data.

I think that rivets would likely have been used - rivets having being used since the Bronze Age to bind everything together. Most Roman siege weapons used torsion power to store the energy that was carried forward, which solely was manpower. Depending on the detail that you need, you may want to as suggested visit the library.

The Romans did have dedicated units for their siege units like a modern military would. It is one of the reasons why the Romans were a successful fighting force, along with their excellent heavy infantry.

Thread necromancy is not allowed in this forum, especially when the first part of the message is just repeating what other said and the second part is wrong, given that the first dedicated siege units only appear in the third/fourth century.