Darius I the Great (r.522-486) was the third Persian emperor of the Achaemenid dynasty, and was a successful leader, despite being best known in the west for the failure of his invasion of Greece (Greco-Persian Wars).
The Persian Empire had been founded by Cyrus II the Great (r.550-529), who had risen from being ruler of the minor province of Persis to take control of the Median Empire (c.550), the kingdom of Lydia (546) and finally Babylon (539). After his death in 529 he was succeeded by his son Cambyses II (r.529-522), whose main achievement was the conquest of Egypt in 525 BC.
Early in his reign Cambyses had killed his brother Bardiya, presumably to secure his own hold on the throne. In 522 BC, with Cambyses still absent after his conquest of Egypt, a revolt against him broke out in Iran, led by someone claiming to be Bardiya. Cambyses gathered his army and began the journey home, but he died on the way, either committing suicide or after suffering an accidental sword wound. This meant that the direct male line of Cyrus was extinct. He many have had up three daughters, although the only one whose name we know, Atossa, was originally married to Cambyses.
Control of the army was seized by Prince Darius, one of Cambyses's generals and a member of the Achaemenid family. At the time of Cambyses's death, Darius was commander of the Immortals, the elite core of the Persian standing army. He was descended from Teispes, the second recorded king of Persis from the Achaemenid dynasty and the first whose existence is generally accepted. Teispes expanded his kingdom and after his death split it between his sons Cyrus I and Ariaramnes. This split in power didn’t last for long - Cyrus I was succeeded by Cambyses I, who was given control of a reunited Persis by the Medes, but Ariaramnes's descendents survived and remained important noblemen. Ariaramnes was followed by his son Arsames and his grandson Hystaspes, neither of whom were considered to have been kings. Darius was the son of Hystaspes and was thus a member of the Royal dynasty, although not closely related to Cyrus I. When the revolt broke out Hystaspes was serving as governor of Parthia, and Arsames was also still alive.
The pretender doesn't appear to have survived long after Darius returned to Iran, and was killed by six senior members of the Achaemenid family who then declared Darius to be the legitimate successor to Cambyses. The wider revolt took longer to put down, but after a year of heavy fighting across the Empire, but especially in Media and Persia, Darius was secure on his throne. There were also two revolts in Babylon, both involving pretenders who took the name Nebuchadrezzar. After the second revolt, in 521, the inner walls of Babylon were demolished, although the city remained an important Persian centre.
Darius married Atossa, the daughter of Cyrus, presumably to increase his legitimacy. Soon after the marriage the couple had a son, Xerxes, who was about 35 when he came to the throne in 486 so was probably born in 521. According to a trilingual inscription carved into the rock at Bisitun (Behistun) Darius fought nineteen battles in the first year of his reign. There were revolts in Susiana, Babylonia, Media, Sagartia, Margiana and possibly Egypt, although Darius's opponents failed to coordinate their efforts. Although he tended to respect local traditions during his reign, Darius could act firmly - he had 3,000 of his enemies in Babylon crucified in 519 after putting down the revolt there.
Darius is best know in the west for his wars with the Greeks, but much of his efforts over his long reign of thirty five years went into organising his empire and setting up a system of laws. His efforts in this area probably helped give the Empire the stability that allowed it to survive for another century and a half after his death despite the failures of many of his successors. He fixed the annual tributes, completed the division of the empire into satrapies, developed trade and completed a canal from the Red Sea to the Nile. He appears to have been popular in Egypt, where he helped restore the income of the temples and imposed fairly light taxation. He also began a series of great building projects, including the palace at Persopolis, built c.528-450 BC. Darius founded Persopolis, which became his main capital, to replace Pasargadae, which was probably too closely associated with Cyrus II, founder of the Empire. He is also said to have organised his army into divisions of 10,000 men, each made up of 1,000 strong battalions, 100 strong companies and 10 strong sections, and to have been the first leader to use scythed chariots. He also changed the status of Cyprus, which had been an independent ally of Persian and instead made it part of the fifth satrapy of the Empire (with Palestine and Syria). He was probably the first Persian emperor to produce his own coinage.
As a military leader Darius had mixed results. His campaigns in the east appear to have been successful, and he claimed control over parts of the northern India. In 519 he defeated the Scythians east of the Caspian Sea, and he expanded the Empire into the Indus Valley.
In the west he was less successful. His first campaign in that area came in 516 and saw him cross the Hellespont into Europe, taking control of much of Thrace (including the area ruled by Miltiades, later the Athenian commander at Marathon). He then led a campaign against the Scythians north of the Danube (c.513). According to Herodotus this expedition involved an army 700,000 strong and 600 ships, with continents coming from Ionia. The Ionians were told to sail two days up the Danube from the Black Sea and then build a bridge of ships across the river. In the meantime Darius led his army into Europe, across Thrace and up to the river. At first he planned to have the bridge dismantled and the Ionians join his army, but he was then persuaded to leave the bridge intact and guarded by the Ionians. They were to wait for sixty days and if the Persians hadn't returned by then to assume that they had been defeated, destroy the bridge and return home. Once he was across the river Darius faced the same problem as most opponents of the nomads - the Scythians refused to stand and fight, and instead kept retreating, just out of reach. The Persians advanced an unknown distance around the Black Sea, but were unable to catch up with their foes. Eventually Darius gave up and pulled out with the best remaining troops. The Scythians beat the Persians back to the bridge, and tried to convince the Ionians to destroy it. They pretended to agree, but after some debate had decided to stick with Darius. When the Persians reached the river it looked as if the bridge was gone, but the Ionians had only temporarily dismantled it. The bridge was restored and Darius made his escape. Darius was able to extract his army intact and retained a sizable foothold on the European side of the Hellespont, occupying parts of Thrace and Macedonia, and the city of Byzantium.
In 500 BC Darius offered his support to a party of Naxian exiles who had already gained the support of Aristagoras, tyrant of Miletus and Artaphernes, satrap of Lydia. The expedition was launched in 499 BC, but ended in failure after a four-month long siege of Naxos had to be abandoned.
In 499 BC the Greek cities of Ionian revolted against Persian control, led by Aristagoras, who was aware that he was vulnerable after the failure of the Naxos expedition. This Ionian revolt seems to have caught the Persians by surprise and the cities were able to expel the Persians. Thrace and Macedonia also had to be evacuated. With Athenian help the Ionians even went onto the offensive in 498. Darius entered into negotiations with them, while preparing for a first counterattack. This failed, and the Ionians were left alone in 496-495. As later history would prove, the Ionian cities were simply too vulnerable to attack by their more powerful eastern neighbours. In 494 a major Persian effort ended in success. The Greek fleet was defeated near Miletus, and one by one the cities fell. Soon afterwards Darius appointed his son-in-law Mardonius as commissioner to Ionia. By 492 Mardonius had regained control of Thrace and Macedonia. In Ionia he suppressed local tyrants and installed democratic regimes in the Greek cities, and soon won them over. When Darius's son Xerxes invaded Greece in 481 he was able to recruit troops in Greek Ionia.
Darius's next target was Greece, and in particular those cities that had supported the Ionian revolt. A first effort in 492 failed after the fleet was destroyed in a storm. The second effort, in 490, was most famous. The Persian army crossed the Aegean and landed on the east coast of Attica. This campaign ended in defeat at Marathon (12 August 490 BC), a defeat that forced the Persians to retreat back out of Greece. Darius began preparations for an invasion on a much larger scale, but he died in 486, before he could carry out his plans.
Darius was succeeded by his son Xerxes I, who had long been groomed for the throne, serving as governor of Babylon. Xerxes was preferred to Darius's older son Artabazanes. Xerxes had to begin by putting down a revolt in Egypt (486-485 BC), but once this was done he was free to concentrate on Greece, leading to the famous campaigns of Thermopylae, Salamis and Plataea.