The tyranny of the wagon equation
Funny.However, I find some assumptions suspect. Unlike rockets, donkeys can consume fuel en-route by grazing. Armies can also consume fuel by hunting, plundering and being "quartered" by their own people. You can make "supply trains" by having small groups of military gather such resources from a closer distance.This is probably fairly accurate for camels and distances in the Saharan desert though, and you'd have to add the weight of water as well!