If the Roman army of 117 AD and the Mongol armies of Genghis Khan were to do battle, what would happen?
There’s an old saw that goes something like this:
Amateurs worry about strategy. Dilettantes worry about tactics. Professionals worry about logistics.
.. Logistics: horses need to eat 1.5% to 3% of their body weight in forage a day. Mongol horses were not large, but factor in 3 – 5 remounts for each Mongol warrior, and a Mongol army starts looking like a plague of locusts that has to move to survive. Mongol armies could not stay in any one place for long, within a brief period all available forage would be consumed and the Mongol army would have to move on or perish.
On the other side, the Roman army was primarily man-powered, not horse-powered. Men eat a lot less than horses and what they do eat is a lot easier to gather and store and protect.