Roman Metal Armour-Polished or Dull?

[Sean Manning]

You could just not use wagons, and load literally everything onto mules. No need for roads then.

In that case you either need to leave things behind, or need a few thousand exta mules ... and pack saddles, and skilled packers. And in the ancient world horses and mules weren't normally used for power on the farm, so rounding up many on short notice was rarely easy. Not to mention that mules may take up more space in your line of march than the carts did, and further slow you down. Bearers or pack animals have advantages over wagons for army transport, but both have their own problems.