Rome grew up as a village at a crossing of the Tiber River on the north-south road in central Italy. It was and remained an agricultural community.
An estimate of the cost of transportation of wheat indicates the crucial importance of sea travel. The cost of transporting wheat 100 Roman miles by land was 55 percent of the value of the wheat whereas transporting it by sea was only 1.3 percent of the value of the wheat. (p. 368 of The Economy of the Roman Empire by Richard Duncan-Jones)