Going off of much later European experience, this depended on the type of traffic. Despite the speed and cost/weight advantages of sea travel, the Habsburg Spa

Going off of much later European experience, this depended on the type of traffic. Despite the speed and cost/weight advantages of sea travel, the Habsburg Spanish empire maintained a land route between their possessions in Italy and the Netherlands [1]. Road travel had the advantage of reliability - more resistant to both natural disasters and to enemy action in war. This was very important for moving military forces through a large empire, which was a very important consideration for a polity like Rome which was constantly moving troops around to fight some revolt, war of expansion, or war of defense. There were also civilian applications - for small, expensive, non-time-sensitive cargoes. In general, see [2] if you're interested in the transportation network of ancient time - see what combinations of weather, transport preferences (passenger carriage vs. donkey, for example, or safer daylight-only sailing vs. more efficient all-day sailing) push traffic onto coastal roads. [1] https://en.wikipedia.org/wiki/Spanish_Road https://en.wikipedia.org/wiki/Spanish_Road [2] http://orbis.stanford.edu http://orbis.stanford.edu EDIT: For example, let's take the example of travel from Aelia Capitolina (Jerusalem) to Tyrus (Tyre/Sur). For a military application (travelling at military march speeds (60km/day) but restricting yourself to daylight sailing for fear of shipwrecks) relative travel speeds depend on weather - roads are better in winter, sea in summer. If you add in transfer time and cost (finding or rendezvousing with ships, cross-loading cargo, hiring porters) then the relative transfer times and costs change yet again. In general, roads were better for: shorter trips, where transfer times and costs dominate; trips involving faster means of land travel, such as military forced marches, passenger travel by carriage, or in the extreme message passing by horse relay; and trips where protection from weather and enemy action (pirate or military) was paramount. Whereas bulk cargo of relatively low value, such as the massive grain shipments from Egypt to Rome, was only practical by sea.