<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>
what was the purpose of the royal road
to facilitate rapid communication throughout his very large empire from Susa to Sardis