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Delian League, before the Peloponnesian War in 431 BC.
The Delian League, founded in 477 BC, was an association of Greek city-states, members numbering between 150 173, to 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 navy for its own purposes. This behavior frequently led to conflict between Athens and the less powerful members of the League. By 431 BC, Athens' 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.