http://www.idbsu.edu/courses/hy101/peloponn/01.htmThe Peloponnesian War - Page 1 of 17
Athens' aim after Plataea was to drive the Persians from the Aegean Sea, but Sparta was not interested in this vigorous and distant foreign policy. So, leadership of the project fell naturally to Athens.
A league was formed in 477, with a common treasury (a war chest)
at the sacred island of Delos. Athens was the dominant member and an Athenian
was always to be admiral of the combined fleet. The other members contributed
men and ships and money. Sparta was not a member. Because the treasury
was kept at Delos, we call this the
Delian League.
The League was successful in its immediate aim of driving the Persians from the northern Aegean. By the later 470s, the League had cleared much of the southern Aegean, too, and some of the League's members began to consider the work complete.