Delian League
The Delian League was a confederacy of Greek city-states, numbering between 150 and 330, founded in 478 BC under the hegemony 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 functioned as a dual—offensive and defensive—alliance (symmachia) of autonomous states, similar to its rival association, the Peloponnesian League led by Sparta.