Darius ascended the throne by overthrowing the legitimate Achaemenid monarch Bardiya, whom he later fabricated to be an imposter named Gaumata. The new king met with rebellions throughout his kingdom and quelled them each time. A major event in Darius’s life was his expedition to punish Athens and Eretria for their aid in the Ionian Revolt and subjugate Greece. Although ultimately ending in failure at the Battle of Marathon, Darius succeeded in the re-subjugation of Thrace, expansion of the empire through the conquest of Macedon, the Cyclades and the island of Naxos and the sacking of the city of Eretria.
Darius organized the empire by dividing it into provinces and placing satraps to govern it. He organized Achaemenid coinage as a new uniform monetary system, along with making Aramaic the official language of the empire. He also put the empire in better standing by building roads and introducing standard weights and measures. Through these changes, the empire was centralized and unified. Darius also worked on construction projects throughout the empire, focusing on Susa, Pasargadae, Persepolis, Babylon, and Egypt. He had the cliff-face Behistun Inscription carved to record his conquests, an important testimony of the Old Persian language.
Darius is mentioned in the biblical books of Haggai, Zechariah, and Ezra–Nehemiah.
Darius I Hystaspes, or Darius the Great, king of Persia [522-486 BCE]. Through his father Hystaspes, Darius belonged to the Achaemenid family, as did Cyrus The Great and his son Cambyses II, but to a different branch of this family. When Cambyses was in Egypt, during the last year of his reign, a certain Gaumata usurped the throne by pretending to be Bardiya, Cambyses’ brother, who had been assassinated secretly before Cambyses started out for his Egyptian campaign in 525 BCE. When Cambyses learned of this usurpation he immediately set out for Persia, but on the way, while in Syria, he died in July, 522 BCE, as the result of either an accident or suicide, leaving no heir. Darius, a distant cousin of Cambyses, at once set out to gain the throne for himself. With some helpers he slew the Smerdis/Gaumāta or false Bardiya in September, 522 BCE, and assumed the kingship. However, he had to fight against a number of other pretenders and rebels. It took more than a year (522-521 BCE) of hard fighting to put down revolts associated with Bardiya’s claim to the throne. Almost every province of the empire was involved in the conflict, including Persia and, most particularly, Media. He finally emerged from the struggle the undisputed ruler of the Persian Empire. The story of his successes was engraved in three scripts and languages (Persian, Babylonian, and Elamite), accompanied by a sculptured relief, into a high rock wall of the Bisitun Mountain, a few miles east of modern Kermanshah.
Darius proved to be a strong and wise ruler. He was tolerant toward other religions and cultures, promoted learning, agriculture, forestation, and the construction of highways. He also built the great palace cities of Susa and Persepolis.
Such activities, however, did not prevent Darius from following an active expansionist policy. Campaigns to the east confirmed gains probably made by Cyrus the Great and added large sections of the northern Indian subcontinent to the list of Persian-controlled provinces. Expansion in the west began about 516 BC when Darius moved against the Hellespont as a first step toward an attack on the Scythians along the western and northern shores of the Black Sea. The real strategic purpose behind this move probably was to disrupt and if possible to interrupt Greek trade with the Black Sea area, which supplied much grain to Greece. Crossing into Europe for the first time, Darius campaigned with comparatively little success to the north of the Danube. He retreated in good order, however, with only limited losses, and a bridgehead across the Hellespont was established.
By 492 BCE Darius made his son-in-law (Mardonius) special commissioner to Ionia. Mardonius had recovered Persian Thrace and Macedonia, first gained in the campaign against the Scythians and lost during the Ionian Revolt. There followed the Persian invasion of Greece that led to Darius’ defeat at the Battle of Marathon late in the summer of 490 BCE. The “Great King” was forced to retreat and to face the fact that the Greek problem, which had probably seemed to the Persians a minor issue on the western extremity of the empire, would require a more concerted and massive effort. Thus began preparations for an invasion of Greece on a grand, coordinated scale. These plans were interrupted in 486 BCE by two events: a serious revolt in Egypt, and the death of Darius.