I don't know. I guess I'm just having trouble comprehending how the bridges and bridgemen survive even ONE assault when in every other piece of fantasy I've ever read and assault like that would fail spectacularly. As I said before, this is the one thing about the book that is causing me to pull my hair out in frustration.
I don't think there would be enough time for the fire thing to work. The Parshendi get off 1-2 volleys before the bridge is laid down I think. So even if they were hit, I don't think they'd easily catch on fire. They don't have sails or anything easily flammable. It's thick wood. I would guess it would be easy to put out a fire on the bridge. Also, in the "bad" runs, they lost 5 out of 20 bridges, which is probably around 150 bridgemen or something which is at least 300 arrows fired (guessing here) and they only have 1-2 tries (I think). So it seems like bridgemen should be able to survive imo.
2 thoughts I have though:
We know the Parshendi provoked the Alethi but we have no idea why. They seemed to have planned the fight on the plains. It could be that they are just giving the Alethi enough resistance so that the Alethi keep fighting, but for whatever reason they don't actually want to win. Breaking the treaty makes no sense with all the information we've been given. I feel like the Parshendi wanted this long drawn out war for some reason. They want the Alethi where they are. If it was too hard for the Alethi, they might not keep fighting, but they could get suspicious if it was too easy. I think the Parshedi are giving just enough resistance to keep going. Although they really don't want to lose the tower, ever, which is why they always bring more people there. Also, once Dalinar and Sadeas joined up, they brought more men to even the match. It really doesn't seem like the Parshendi are trying to "win", just stall.
Has anyone seen the Parshendi burn the bridges? Or do they just assume it was them? Could something else want it to not be super easy for the Alethi so they burn just enough bridges to make them work building new ones? With all the scouts searching for the chasmfiends, which we know they still do at night, how has no one seen the Parshendi burning the bridges (or have they and I missed that?)