The Delian League, founded in 478 BC, was an association of Greek city-states, numbering between 150 and 330, under the leadership of Athens, whose purpose was to continue fighting the Persian Empire after the Greek victory in the Battle of Plataea at the end of the Second Persian invasion of Greece. The League's modern name derives from its official meeting place, the island of Delos, where congresses were held in the temple and where the treasury stood until, in a symbolic gesture, Pericles moved it to Athens in 454 BC. Shortly after its inception, Athens began to use the League's funds for its own purposes, which led to conflicts between Athens and the less powerful members of the League. By 431 BC, the threat the League presented to Spartan hegemony combined with Athens's heavy-handed control of the Delian League prompted the outbreak of the Peloponnesian War; the League was dissolved upon the war's conclusion in 404 BC under the direction of Lysander, the Spartan commander. Background The Greco-Persian Wars had their roots in the conquest of the Greek cities of Asia Minor, and particularly Ionia, by the Achaemenid Persian Empire of Cyrus the Great shortly after 550 BC. The Persians found the Ionians difficult to rule, eventually settling for sponsoring a tyrant in each Ionian city. While Greek states had in the past often been ruled by tyrants, this form of government was on the decline. By 500 BC, Ionia appears to have been ripe for rebellion against these Persian clients. The simmering tension finally broke into open revolt due to the actions of the tyrant of Miletus, Aristagoras. Attempting to save himself after a disastrous Persian-sponsored expedition in 499 BC, Aristagoras chose to declare Miletus a democracy. This triggered similar revolutions across Ionia, extending to Doris and Aeolis, beginning the Ionian Revolt. The Greek states of Athens and Eretria allowed themselves to be drawn into this conflict by Aristagoras, and during their only campaigning season (498 BC) they contributed to the capture and burning of the Persian regional capital of Sardis. After this, the Ionian revolt carried on (without further outside aid) for a further five years, until it was finally completely crushed by the Persians. However, in a decision of great historic significance, the Persian king Darius the Great decided that, despite having subdued the revolt, there remained the unfinished business of exacting punishment on Athens and Eretria