Herodotus called the Persian king’s official route linking Sardis with Susa the Royal Road.
The road crossed Anatolia and connected the western regions of the Achaemenid Empire with the royal center at Susa. It was designed for rapid movement of royal messengers, administrators, and military personnel. Herodotus famously described relay stations and the speed at which messages could travel along the route.
The Royal Road was not necessarily one perfectly paved highway running continuously across the empire. It was a maintained network of routes, stations, bridges, and services that supported imperial communications. Some sections followed or improved older roads used by the Assyrians, Lydians, and other states.
Sardis was the former capital of Lydia and a key western administrative center. Susa, in southwestern Iran, was one of the Achaemenid royal residences. The route therefore joined two strategically important ends of the empire rather than connecting every Persian capital.