Taming the Onager

[D B Campbell]

(In case you think this point is obvious, the French scholar Jacques Fontaine managed to sketch the machine without cross timbers, so that the ropes really are all that holds the sides apart!)

I tried hard to imagine that but failed! Could you please share any definition or an image of it?

Here is Fontaine's reconstruction. It seems that the axles for the wheels (neither element mentioned by Ammianus!) are all that keep the frame from falling apart!
[attachment=8408]Fontaine_1977_Fig02.jpg[/attachment]

I like to think that I "rediscovered" De Reffye's excellent interpretation of the onager (in my Osprey book, p. 32, plate G; it can also be seen in Hesperia 80.4 (2011), p. 691 fig.4). mile: Until then, everyone seemed to use Payne-Gallwey's version.

[Koyuncu]

I must say I am disappointed with Fontaine's reconstruction because I was expecting a frame solely depends on ropes. Still, I am grateful to you for sharing the picture.

Back to topic, I disagree with several points about the design proposed by P. Clodius Secundus (Randi Richert).

First, in my humble opinion, we must admit that Ammianus is either confused with some features of weapons or missed some parts.

Ammianus's first pharagraph;

The scorpion, which is now-a days called the wild ass, has the following form. Two posts of oak or holm-oak are hewn out and slightly bent, so that they seem to stand forth like humps. These are fastened together like a frame-saw and bored through on both sides with fairly large holes. Between them, through the holes, strong ropes are bound, holding the machine together, so that it may not fly apart.

LCorneliusScaeva, (Jim Miller) is right that there is a rigid frame, as mentioned as frame saw. I tried to research about Roman saws and found Roman Woodworking by Roger Brandley Ulrich. In his book, he provides some manuscripts about frame saws used by Romans. Hence, it is not needed to worry about rigid base in case of historical literal evidence in my humble opinion.
Here the related section of book with some visuals;

Related part of text about throwing arm;

From the middle of these ropes a wooden arm rises obliquely, and being set upright in the manner of a yoke-pole, and is twined around with cords in such a way that it can be raised higher or depressed. To the top of this arm, iron hooks are fastened, from which hangs a sling of hemp or iron. In front of the arm is placed a great cushion of hair-cloth stuffed with fine chaff, bound on with strong cords, and placed on a heap of turf or a pile of sun dried bricks; for a heavy machine of this kind, if placed upon a stone wall, shatters everything beneath it by its violent concussion, rather than by its weight.

I think Ammianus here, defines the position of throwing arm not the shape of arm. Imagine an onager with released arm and a cart without hitched animals. The yoke pole will stand above ground with a slight degree just like onager's arm resting over buffer.

Also, about connecting the sling after arm is bend is contradicts with the text as Ammianus while describing throwing arm says;

From the middle of these ropes a wooden arm rises obliquely, and being set upright in the manner of a yoke-pole, and is twined around with cords in such a way that it can be raised higher or depressed. To the top of this arm, iron hooks are fastened, from which hangs a sling of hemp or iron.

So sling is fastened to arm before projectile is placed on the sling. Ammianus in this case a bit confusing.

In conclusion, in my humble opinion, there is some points at least to be examined more closely and with more evidences supported by other sources.