Darius ascended the throne by overthrowing Gaumata, the alleged magus usurper of Bardiya with the assistance of six other Persian noble families; Darius was crowned the following morning. 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 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.
Dārīus and Dārēus are the Latin forms of the Greek Dareîos (Δαρεῖος), itself from Old Persian Dārayava(h)uš (𐎭𐎠𐎼𐎹𐎢𐏁; in Aramaic dryhwš), which is a shortened form of Dārayava(h)uš (𐎭𐎠𐎼𐎹𐎺𐎢𐏁). The longer form is also seen to have been reflected in the Elamite Da-ri-(y)a-ma-u-iš, Babylonian Da-(a-)ri-ia-(a-)muš, Aramaic drywhwš, and possibly the longer Greek form Dareiaîos (Δαρειαῖος). The name is a nominative form meaning "he who holds firm the good(ness)", which can be seen by the first part dāraya, meaning "holder", and the adverb vau, meaning "goodness".
At some time between his coronation and his death, Darius left a tri-lingual monumental relief on Mount Behistun, which was written in Elamite, Old Persian and Babylonian. The inscription begins with a brief autobiography including his ancestry and lineage. To aid the presentation of his ancestry, Darius wrote down the sequence of events that occurred after the death of Cyrus the Great. Darius mentions several times that he is the rightful king by the grace of Ahura Mazda, the Zoroastrian god. In addition, further texts and monuments from Persepolis have been found, as well as a clay tablet containing an Old Persian cuneiform of Darius from Gherla, Romania (Harmatta) and a letter from Darius to Gadates, preserved in a Greek text of the Roman period.