The pants flotation was taught until recently and probably still is.
One thing about crossing water in cold places like Europe during winter is that you do it naked to keep your clothes dry, because of hypothermia, once you cross, you dress.
The use of bales straw to cross rivers en masse has been used all the way up into modern times, but perhaps the first documented use of a related method was by Alexander the Great, to move his entire force across a river in India.
I think that was the same battle where he’d figured out how to deal with a large number of war elephants. Probably coming up with that idea was why he decided to get his army across during the night to try it out.
Use of African elephants as a sort of ancient tank was dealt with in the same way, thanks to A the G’s tactics having been taught in ancient military academies; last known large use of African elephants in combat was at Thapsus if memory serves. Not sure it was ever all that common.