<P> The Royal Road was an ancient highway, part of the Silk Road and the Uttara Path built in ancient South Asia and Central Asia, reorganized and rebuilt by the Persian king Darius the Great (Darius I) of the first (Achaemenid) Persian Empire in the 5th century BCE . Darius built the road to facilitate rapid communication throughout his very large empire from Susa to Sardis . Mounted couriers of the Angarium could travel 1677 miles (2699 km) in seven days; the journey from Susa to Sardis took ninety days on foot . The Greek historian Herodotus wrote, "There is nothing in the world that travels faster than these Persian couriers ." Herodotus's praise for these messengers--"Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds"--was inscribed on the James Farley Post Office in New York and is sometimes thought of as the United States Postal Service creed . </P> <P> The course of the road has been reconstructed from the writings of Herodotus, archeological research, and other historical records . It began in Asia Minor (on the Aegean coast of Lydia, about 60 miles east of İzmir in present - day Turkey), traveled east through what is now the middle northern section of Turkey (crossing the Halys according to Herodotus), and passed through the Cilician Gates to the old Assyrian capital Nineveh (present - day Mosul, Iraq), then turned south to Babylon (near present - day Baghdad, Iraq). From near Babylon, it is believed to have split into two routes, one traveling northeast then east through Ecbatana (in present - day Iran) and on along the Silk Road, the other continuing east through the future Persian capital Susa (in present - day Iran) and then southeast to Persepolis . Of course, such long routes for travellers and tradesmen would often take months on end, and during the reign of Darius the Great numerous royal outposts (Caravanserai) were built . </P>

What was the purpose of the royal road