The Royal Road was an ancient highway reorganized and rebuilt by the Persian king Darius the Great (Darius I) of the first (Achaemenid) Persian Empire in the 5th century BC. Darius I built the road to facilitate rapid communication on the western part of his large empire from Susa to Sardis. 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.
The course of the road has been reconstructed from the writings of Herodotus, archeological research, and other historical records.
Because the road did not follow the shortest nor the easiest route between the most important cities of the Persian Empire, archeologists believe the westernmost sections of the road may have originally been built by the Assyrian kings, as the road plunges through the heart of their old empire. More eastern segments of the road, identifiable in present-day northern Iran, were not noted by Herodotus, whose view of Persia was that of an Ionian Greek in the West; stretches of the Royal Road across the central plateau of Iran, such as the Great Khorasan Road, are coincident with the major trade route known as the Silk Road.
However, Darius I improved the existing road network into the Royal Road as it is recognized today. A later improvement by the Romans of a road bed with a hard-packed gravelled surface of 6.25 m width held within a stone curbing was found in a stretch near Gordium and connecting the parts together in a unified whole stretching some 1677 miles, primarily as a post road, with a hundred and eleven posting stations maintained with a supply of fresh horses, a quick mode of communication using relays of swift mounted messengers, the kingdom's pirradazis.
In 1961, under a grant from the American Philosophical Society, S. F. Starr traced the stretch of road from Gordium to Sardis, identifying river crossings by ancient bridge abutments. It was maintained by personal guards.[clarification needed]
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.
Euclid is said to have replied to King Ptolemy's request for an easier way of learning mathematics that "there is no Royal Road to geometry", according to Proclus. The same sentence is also attributed to Menaechmus replying to Alexander the Great.
Charles Sanders Peirce, in his How to Make Our Ideas Clear (1878), says, "There is no royal road to logic, and really valuable ideas can only be had at the price of close attention."
Sigmund Freud famously described dreams as the "royal road to the unconscious" ("Via regia zur Kenntnis des Unbewußten").
Karl Marx wrote in the 1872 Preface to the French Edition of Das Kapital (Volume 1), "There is no royal road to science, and only those who do not dread the fatiguing climb of its steep paths have a chance of gaining its luminous summits."
The Royal Road to Romance (1925) is the first book by Richard Halliburton, covering his world travels as a young man from Andorra to Angkor.
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