The Achaemanide map showing the boundries of the empire that Cyrus II initiated and Darius I consolidated. Below is listed some of the great achievements of the Persians during the Achaemenide Period, some world firsts.
The following is taken from 'the Dazzling Reach of Darius's Imperial Spear' Time life Books.
Suez Canal workers, digging 20 miles north of Suez in 1866 came upon fragments of a red granite stele that, whole, had stood nearly 10' tall and measured about 7' across. Startled at finding the monument, the workmen would have been even more surprised had they been able to read the inscriptions on its sides, spelled out in Old Persian, Babylonian, Elamite, and Egyptian. These included an astonishing message- repeated in all four languages- from Darius the Great, King of Persia: "I ordered this canal to be dug from the Nile, which flows in Egypt, to the sea that goes to Persia." This canal was dug out as I commanded," he boasts on his stele, "and ships went from Egypt through this canal into Persia as was my desire." According to Herodotus, the canal was wide enough for two war galleys to pass each other under oar. Ships took four days to move from one end to the other.
The empire that Darius acquired and extended united western Asia from the Mediteranian to the Indus Valley under a single ruler ( see above) covering an area almost two million square miles, with some 10 million inhabitants.
Other achievements of note of the Achaemenids is the road built between Susa in southern Iran to Sardis in Lydia (the Royal Road). Herodotus had calculated that it took Cyrus three months to move his army from Susa to Sardis, a journey of some 1700 miles. Cyrus is also reputed to have devised the first postal system. Xenophon reports that Cyrus first calculated the distance a horse could go in one day without being too exhausted, he than had a series of posting stations built distances of one horse-day apart, hence ensuring efficient flow of information between the king and provincial governors.