Iranians expanded the trade; from China in the east, to Asia Minor and Mesopotamia in the west, to the Iranian plateau and the Indus valley in the south.
An east-west distance of nearly ten thousand kilometres. The Iranian trade routes, would come to be known as the Silk Roads. Amongst the different Indo-Iranian groups, the Sogdians would become the principle traders along the Silk Roads.
Herodotus (Histories 5.52-54) gives us his account of the Persian empire's roads which he called the Royal Roads. He was familiar with the western Royal roads which he had travelled and which ran from Lydia (Western Asia Minor) at the borders of Ionia and Greece to Susa.
These roads passed through Armenia, the Tigris River and Babylon. Branches ran from Susa to Persepolis in Persia, and from Babylon to Ecbatana (Hamadan) in Media and beyond to Ragha and the eastern empire, and the Indus valley.
Herodotus (5.52-54) informs us "Now the true account of the road in question is the following: Royal stations exist along its whole length, and excellent caravanserais; and throughout, it traverses an inhabited tract, and is free from danger." The road was well maintained, guarded and traversed by a regular courier and postal service.
In book 8.98, Herodotus talks about the couriers. This was the first Postal System in the world.
"Nothing mortal travels so fast as these Persian messengers. The entire plan is a Persian invention; and this is the method of it. Along the whole line of road there are men (they say) stationed with horses, in number equal to the number of days which the journey takes, allowing a man and horse to each day; and these men will not be hindered from accomplishing at their best speed the distance which they have to go, either by snow, or rain, or heat, or by the darkness of night. The first rider delivers his despatch to the second and the second passes it to the third; and so it is borne from hand to hand along the whole line, like the light in the torch-race, which the Greeks celebrate to Vulcan. The Persians give the riding post in this manner, the name of 'Angarum.'" (The angarum were called pirradazish by the Persians).
For the first time in recorded history, travellers and traders could traverse the entire Persian empire relatively quickly and safely with a uniform law to protect them. Trade flourished and the revenues helped to make the Persian empire one of the wealthiest known to history.
