The Persian Empire arose in the mid-6th century when Cyrus, the first Persian king, seized power in the kingdom of the Medes. The Persians had done very well since then. In a short time, they built an empire that reached from the Aegean to the Indus and from the Danube to the Red Sea. It was the largest empire that the world had seen. During the reign of Darius I (521-486 BC), a usurper born of a branch of the royal family, the Persian lands were consolidated. Darius also wished to enlarge his empire, rounding off its borders, in India, to the east of the Caspian Sea, in Armenia, Northern Africa, and in the Aegean. It was in this last-mentioned area that Persians and Greeks were to clash with each other over Persian expansionism.
Darius was a great organizer, and attempted to knit the heterogeneous collection of peoples who inhabited his empire into some kind of unity. To this end, he promulgated new laws that were a return to the laws of Hammurabi, created a uniform government, standardized weights and measures, and reformed the coinage. Even the Old Persian script, a syllabary making use of cuneiform, is supposed to have been created expressly for the use of Darius, who wanted his official inscriptions to be composed in writing comparable to Assyrian and Babylonian examples. However, the increasing use of Aramaic as the lingua franca for the whole empire was in the end of much greater importance. The building of a new capital, Persepolis, can be considered a symbol of the many changes taking place under Darius. The king was also a follower of Zoroaster, and favored Zoroaster’s dualistic teachings without rejecting other religions. The growth of Persian dualism fits into a general trend, in which traditional religions that were exclusive to certain areas or towns were coming to be replaced by teachings of universal scope, such as Babylonian astrology and Jewish monotheism.
The immense Persian Empire was divided into provinces, over 20 so-called satrapies governed by satraps, literally “protectors of the kingdom.” Cyrus had been the first to copy the Assyrian practice of turning conquered areas into provinces. Darius continued this policy. The satrapies had to pay tribute, which Darius converted from an irregular tax into a regular, yearly levy. The center kept a measure of control over the outlying areas by stationing in every satrapy civil and military magistrates who were answerable to the king, and by annually sending out inspectors. But otherwise the satraps were relatively autonomous rulers who recognized the overlordship of the Persian king.