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. The construction of the road as improved by Darius was of such quality that the road continued to be used until Roman times. A bridge at Diyarbakır, Turkey, still stands from this period of the road's use. The road also helped Persia increase long-distance trade, which reached its peak during the time of Alexander the Great (Alexander III of Macedon). 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. The road also was made secure by the Persians. Guard posts were stationed along the road, patrols were also made to secure the route. The Royal Road would be a monument of the Persian Empire. Legacy 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. A metaphorical "Royal Road" in famous quotations 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. 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." This essay was claimed by William James as instrumental in the foundation of the philosophical school of pragmatism. 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.