Whilst reading s topic somewhere about 5-600 lb draw-weight crossbows, I got to thinking. With reference to crossbows made in the medieval era, or of materials only available in that era .. is there a *theoretical* MAXIMUM poundage for such a weapon ? I suspect that it would have been possible to make bow itself of a very high poundage, but there must have been a limit lower than that because of the need for a bowstring to sustain the shock of firing it ? Mechanically spanning the bow could be done but the shock of firing would snap any material of the period ?

My two cents... I think it's just carrying the crossbow. There are siege crossbows that fire bolts the size of spears, and you can spin rope however thick you need, but at some point it becomes too bulky to carry, lift and aim.

In this days I'm starting to draw my own crossbow, so it's a problem I have affronted a bit.

What is the difference between a crossbow and a siege crossbow?

I would suggest that we define a crossbow as capable to be fired standing without support, even if clumsily, whereas a siege engine is necessarly mounted on a rack, wheels or wall. So, as Matthew said, the problem became the weight.

Defined a weight (if someone has tried free shooting very heavy crossbows he can give us an idea) you have to calculate how much weight you have to give to the stock and how much to the prod.

Heaviest number I've seen for a crossbow that can be carried by one man is 4200 pounds. I don't remember where I got that from, however, and if the number is true then that thing must have taken forever to span!

As far as spanning goes, I'm curious as to the amount of force required to wind or crank heavy crossbows. According Payne-Gallwey, a child can span a siege crossbow with a windless. Did some technical limitation prevent them from using higher ratios? Given that earlier spanning methods relied on strength, it seems like it would have been better to have devices that required more brawn in exchange for greater speed or power.