Roads played a major role in military, adminstrateive, and also conceptual domination of the Roman Empire. They were created and equipped when the conquest took place, and were abandoned when Roman ocupation collapsed.
Roads played a determining role in the creation of a centralized administrative system. [imperial postal service] was improved many times and performed the dual function of allowing imperial functionaries to travel around, and dispatches to be delivered with the minimum of delay. The staging posts also played an essential part in allowing ordinary travelers to move around the empire, in which personal mobility was becoming more commonplace. pp. 44-45.
The great majority of cargo was moved by water which was faster and cheaper than transporting goods by road. ... at the end of AD 301 we may calculate that to transport a cargo of corn over 100 miles cost 1 per cent of its overall value if carried by sea, 4.9 per cent if shipped by river, and 28 per cent (or even 56 percent depending on how the document is interpreted). These proportions were very close to those noted for eighteen-century England. p. 45.