The Ionian Revolts were triggered by the actions of Aristagoras, the tyrant of the Ionian city of Miletus at the end of the 6th century BC and the beginning of the 5th century BC. They constituted the first major conflict between Greece and Persia.
The Revolt of Naxos
In 502 BC, the people of Naxos, an island in the Aegean Sea controlled by the Persian Empire, revolted. The former rulers of Naxos appealed to Aristagoras, the Greek tyrant of the Ionian city-state of Miletus, for aid. Aristagoras agreed, hoping to annex Naxos for himself once the conflict was resolved.
In order to prosecute the campaign, Aristagoras, in turn, sought out the aid of Artaphernes, the satrap of Lydia and brother to Darius I of Persia. Artaphernes agreed to supply Aristagoras with a fleet of ships under the command of the esteemed Persian admiral Megabates. In order to secure the alliance, however, Aristagoras not only offered to share with Artaphernes the spoils of annexing Naxos, but also promised to reduce the Cyclades and perhaps Euboea herself. This was a promise Aristagoras could not keep unless the expedition were successful.
While preparing for the campaign, however, Aristagoras managed to offend Megabates, and the admiral secretly informed the Naxians of the coming invasion. As a result, when the fleet arrived, they were met with unexpected preparation and resistance. In 499 BC after four months, the abortive expedition was forced to retreat.
The Ionian Revolt
With the failure of his attempt to intervene in Naxos, Aristagoras found himself in dire straits: unable to repay Artaphernes, he had alienated the Persian government and placed himself in imminent danger. In a desperate attempt to save himself, Aristagoras chose to incite his own subjects, the Ionian Greeks, to revolt against their Persian masters. He was also aided by his father-in-law Histiaeus, the former tyrant of Miletus who was now an advisor to Darius.
In 499 BC Aristagoras called a council of the leading citizens of Miletus and laid out a plan of rebellion. They all came to support idea of revolt, except (famously) for the historian Hecataeus. Aristagoras, who had already dispatched soldiers to arrest the leaders of Mylasa, Termera, and Mytilene, laid down his Persian governorship, and the city adopted a democratic form of government.
The revolt spread quickly through the whole of Ionia, and the Greeks had soon found universal freedom from the Persian governors/tyrants. They realized, however, that the Persian Empire would soon be sending a military expedition to reclaim their cities. As a result, Aristagoras travelled to Greece in an effort to garner support. There he repeated his former tactics of offering money he did not have, alienating Sparta, but gaining the support of Athens and Eretria.
The Sack of Sardis
An Athenian and Eretrian fleet sailed Athenian troops to Ephesus. There they joined with a force of Ionians and marched upon Artaphernes' capital of Sardis. Artaphernes -- who had sent most of his troops to siege Miletus -- was taken by surprise. Despite his disadvantage, however, Artaphernes was able to retreat to the citadel and hold it. Although the Greeks were unable to take the citadel, they were free to pillage the town. During the pillaging, fires set throughout the city spread out of control and burned Sardis to the ground.
(It is said that when Darius, the Persian Emperor, heard of Sardis being burnt by the Athenians he swore vengeance upon them, and tasked a servant with reminding him three times each day of his vow. In some accounts, Darius is entirely unaware of the existence of Athenians before the attack -- so vast was the Persian Empire, and so minor were the Greek peoples.)
Having met with some measure of success, the Greek troops were forced to return to Ephesus as Persian reinforcements approached. On their way, however, they were ambushed by the Persian army and disastrously defeated. The Athenian troops rapidly effected a retreat onto their vessels, and returned to Greece.
The Revolt Spreads
The End of the Revolt
Although, for a time, it appeared that the Greek city-states had earned their independence, in reality there was no way they could resist the might of the Persian Empire, and this now turned solidly against them. Cyprus was the first to be crushed, and siege was subsequently laid to most of the other cities along the coast. At this point, Aristagoras abandoned the revolt and fled to Thrace.
By the sixth year of the revolt (494 BC), Artaphernes had successfully captured several of the revolting city-states and was now laying siege to Miletus. In 494 BC, the decisive Battle of Lade was fought at the island of Lade, near Miletus' port. Although out-numbered, the Greek fleet appeared to be winning the battle until the ships from Samos and Lesbos retreated. The sudden defection turned the tide of battle, and the remaining Greek fleet was completely destroyed. Miletus surrendered shortly thereafter, and the Ionian Revolt came to an end.
A year after the capture of Miletus, The Capture of Miletus -- a play by the poet Phrynichos -- was performed in Athens, reducing the entire amphitheater to tears. The Ionian Revolt, although ultimately a failure for the Ionian Greeks, was a touchstone for both Persia and Greece. As such, it marks the beginning of the Persian Wars.