Roman crossbow

[Thomas V.]

Bogfinds are flatbows of ash and elm, these are nice springy woods which make great bows. [...] Yew just isn't indignious to north europe so as a bowwood would have been unknown ...

The bows from the Nydam bog are are yew bows with a D-shaped cross section.

Yew also grows slowly, so to get bowstaves from a yew, it is quartered, at least split into triangular sections with the pointy end toward the center. When you shave off that point, hey presto, there is the D shape you want for your bow. The back of the bow (for non archers, the side away from the archer) is stripped of bark and hardly worked at all, just smoothened. Should you try to turn a yew bowstave into a true flatbow, you will violate the grain and seriously weaken the bow.

Actually it's the other way round: The straigth part of the "D" (back of the bow) is an intact growth ring, the belly is rounded by the bowyer. You can turn a yew stave into a flatbow without violating the grain of the back of the bow; you just have to make a flat belly instead of a rounded one.

I don't deny the existence of ash bows, by the way. However, given the Germanic bog finds from the Roman era, my opinion is that said finds, (mainly :?) "D"-shaped yew bows, are the best basis for reconstructing Roman self bows.

Apart from this, even if Roman self bows should have been of ash, it's quite unlikely that this matters in terms of the arcuballista, as the depictions strongly indicate composite bows.