Cyrus the Great created an organized army including the Immortals unit, consisting of 10,000 highly trained soldiers[REF] Cyrus also formed an innovative postal system throughout the empire, based on several relay stations called Chapar Khaneh [REF].
The satrapies were linked by a 2,500-kilometer highway, the most impressive stretch being the Royal Road from Susa to Sardis, built by command of Darius I.