The Royal Road was an ancient highway reorganized and rebuilt for trade by Darius the Great, the Achaemenid emperor, in the 5th century BC.[1] Darius I built the road to facilitate rapid communication on the western part of his large empire from Susa to Sardis.[2] Mounted couriers of the Angarium were supposed to travel 1,677 miles (2,699 km) from Susa to Sardis in nine days; the journey took ninety days on foot.[3]