Questions and Answers about the Onager
What is the real history of these war machines?
Actually, we don't have a lot to go on. At the end of the 19th century, the nobleman and amateur historian Ralph Payne Gallwey wrote a book about the crossbow, and in it he describes the "catapult", what modern historians call a mangonel or onager.
Unfortuantely, we now know that most of his sources are fiction. He even invented fake reference numbers for them at the Bibliothec National in Paris, France.
The books of Violet Le Duc (1814-70) were also a large influence on Gallwey, however Violet's machines are pure invention. There are only two pictures of machines of this type and both are far too vague to be of any use. There is also a brief description by the Roman engineer Vitruvius (Wikipedia link) of a Roman Onager.
Below is the most detailed description of the Mangonel to survive the ages. It is Eric Marsden's translation of a text written by Ammianus Marcellius in the 4th century AD.
The design of the scorpion, which they now call the onager, is as follows. Two beams of oak or holm-oak are fashioned and given a moderate curvature so that they seem to bulge into humps, and the beams are connected as in a frame saw, having quite large holes bored in each side; between these beams, through the holes, powerful ropes are stretched, preventing the structure from falling apart. From the middle of the cords a wooden arm rises at an angle and, being set upright in the manner of a yoke-pole, is so inserted in the twists of sinew that it can be raised higher and lowered; to its tip iron hooks are fastened, from hangs a sling of two or iron. A huge buffer is padded in front of the arm, a sack stuffed with fine chaff, secured by strong binding. The engine is placed on piles of turf or brick platforms. You see, if put on a stone wall, a mass of this sort smashes whatever it finds underneath because of the violent recoil, not its weight. When it comes to combat, a round stone is put in the sling and four young stalwarts on each side, by pulling rearwards the bars to which the withdrawal ropes are connected, draw the arm down almost horizontal; finally, when all this has been done, and only then, the master artilleryman, standing loftily beside it, strikes the pin, which secures the ropes of the whole machine, with a heavy hammer; whereupon the arm, released by the sharp blow and meeting the softness of the sack, projects the stone which will smash whatever it hits. It is called a torsion engine because its whole power is derived from torsion, and scorpion because it has an upraised sting; modern times have also applied the name of onager to it because wild asses, when hunted in the chase, throw up stones so high behind their backs by kicking that they penetrate the chests or their pursuers or actually break their bones and smash their skulls.
This is the best description surviving the ages regarding Onager construction,
Is a Mangonel the same as an Onager?
Yes and no.
If you went back in time, and asked someone to show you an Onager, they would probably show you a wild donkey. Onager was the name for an untamed donkey, but the name was also used for the Roman mangonel since the back end of the machine "kicks" when it is fired, just like a wild donkey kicks and bucks when a rider tries to mount it.
The word Mangonel comes from the ancient Greek word "Manganon", meaning "engine of war" and covers a variety of ancient artillery types.
Shouldn't it have a sling on the end of the arm?
Yes, and probably also no.
In a lot of ancient depictions, the mangonel is drawn with a big spoon or bucket on the end of the throwing arm. This is also true of most catapults you see in Hollywood movies. The fact is, a sling is much more effective at throwing a stone than a spoon is.
In one historical reference, they use the term "scorpion" and "onager" for the same machine. It's like an Onager for the way it kicks, and the iron sling-hook on the end of the arm resembles a scorpion's stinger on the end of his tail. The iron hook was the sling attachment, not a spoon!
The advantage a bucket has over the sling is that it's easier to load, easier to aim, and you can load more than one projectile in the bucket. A sling would scatter them way too much, but a bucket full of stones would make an effective anti-personnel weapon, especially at moderately close range.
Keep in mind that these were military weapons. The armies didn't want the enemy to learn how to build one properly. So whenever anyone made a diagram or described the machine, they would leave out key details. Sometimes the artist would fill in the gaps with his own imagination. The fact is, we don't really know for sure what they looked like.
How does an Onager differ from a catapult?
An Onager is a type of catapult.
The term "catapult" is used to describe all of the different types of throwing machines. Even a slingshot or the hydraulic machines used to hurl planes off the front of aricraft carriers are called catapults.
The three most common types of ancient catapult are the Greek Ballista, the Roman Onager, and the Medieval Trebuchet. And there are an abundance of minor types.
What kind of ropes did the Greeks and Romans use?
The Romans and Greeks probably used horse hair, and when there wasn't enough of that, it has been said that they used human hair. Everyone in an entire township would have to shave their heads for the war effort. The hairs would be spun into ropes, and bundled together to make skeins of hair about 1 foot thick and several feet long.
There is actually some debate about this among historians. Some believe that animal sinew and even leather was more likely used. But the ancient people were pretty smart about natural materials, and from an engineering perspective, hair is a better material. It's also a lot easier to get in rope-making quantities than sinew.
In fact, hair is actually much stronger than steel in a pound-for-pound comparison, and it is also extremely elastic. It was, and still is the best thing around for powering Onagers. Modern reconstructions of Onagers typically use nylon and polypropylene ropes. These are good choices, but are still inferior to bundles of hair.