A subway-style diagram of the major Roman roads, based on the Empire ca. 125 AD

https://sashatrubetskoy.github.io/romanmap/

Edit: I am not the author, I'm too old for this :)

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

[2] 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.

https://en.wikipedia.org/wiki/Samosata is the modern city of Samsat https://en.wikipedia.org/wiki/Rhesaina is Ressaina (see http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:19...) https://en.wikipedia.org/wiki/Zeugma,_Commagene Zeugma is near modern-day Gaziantep

The location of historic Tharrana is apparently not finally known. Harran, Turkey is one possibility mentioned at http://www.euratlas.net/cartogra/peutinger/10_mesopotamia/me....

Since all reference points are in Turkey or Syria, best guess is that the cirular lake with the island is Al Jaboul Lake, 36.024360"N, 37.610087"E. It used to be a tributary to the Euphrates but no source I could find states exactly when that changed.

I understand that fighting piracy was a political problem. Pirates were mobile, and while any commander could suppress piracy in any area those not caught would move elsewhere and return when the commander's imperium was over and he had to return to Rome to give account.

It was feared that an admiral who was given an imperium for the whole of the Mediterranean would have such power that he would use it for political ands and upturn the system. So piracy grew with Roman hegemony, and when the seas had become so unsafe that the security of the grain supply was a political issue something had to be done. It turned out that the fears were well-founded, Pompeius was given his imperium maius over all the Mediterranean and 50 miles inland, he squashed piracy, and the First Triumvirate followed.