As the Behistun Inscription makes clear, Darius believed that his rulership was a reflection of the heavenly order controlled by Ahura-Mazda. This basic idea, a common theme in many kingdoms, relates to the concept of legitimacy. For example, the Israelite kings were judged on the basis of whether they followed the guidance of Yahweh and his prophets; likewise the chinese believed their emperor to be the "Son of Heaven,” whose rule would come to an end if he defied the gods.
Just as Darius believed that there were laws governing heaven and that his leadership was in line with those laws, he worked to establish an earthly order. The Persians created by far the most organized empire that had existed up to that time. to the superior military strength of the Persian army, it was seldom necessary for Darius to actually send in his troops
To bring a group of subject peoples into line. The threat of military action was enough.
Besides, even under the less open-minded Darius, Persian rule was not perceived as a hardship by most of the conquered nations. In the area of law, Darius set out to establish a system of justice that would be uniform, or the same, throughout the empire, yet would also take into account local customs. Under his legal reforms, the provinces had two types of courts: one court to administer law under the Persian legal code and one court to deal with local matters according to the local system. In theory, this is not so different from the legal system in the United States today: a person who breaks the law may be charged under the local, state, or federal laws, depending on the nature of the crime.
The system of satrapies (SA-trap-eez), or provinces, also allowed a measure of local rule. The Persian Empire was divided into about twenty satrapies, each ruled by a satrap, or governor. The satrap, who was usually a member of the royal family, had a free hand in ruling his local area, but of course he was expected to remain loyal to the emperor in Susa (SOO-suh), the Persian capital.
Susa lay at the end of the “Royal Road,” which ran for 1,500 miles from Sardis [see sidebar, “'The Royal Road' and the Persian Postal System”], but Darius built his palace and many other great structures at Persepolis (pur-SEP-oh-liss) to the southeast. Not only was the Royal Road a great feat of engineering in itself, but it made possible the world's first real postal system. The Persians also dug a canal between the Nile River in Egypt and the Red Sea to the east.