Roman roads did not remove the need for waterborne transport on the scale required to sustain armies. The Danube connected frontier forts and allowed large quantities of supplies to move between them. Grain, wine and metal cargoes were more efficiently carried by boat than by carts. Access through the Black Sea could also avoid difficult routes across mountains. A defensible river frontier therefore offered a supply route alongside its military barrier.
Notable Point · 26:46-29:31
Why Roman supply followed the Danube despite the road network
Water transport linked Roman frontier forts and carried bulky supplies more efficiently than carts, while the Black Sea offered an alternative to mountain routes.