Delos was the most important Panhellenic sanctuary, and, according to mythology, the birth-place of Apollo and Artemis. The first signs of habitation on the island date from the 3rd millenium B.C., and important remains of the Mycenaean period have been uncovered in the area of the sanctuary. In the 7th century B.C. Delos was already a known Ionic centre because of its religious importance as the birth-place of Apollo. Athenian influence was initiated on the sanctuary with the first purification of Delos by Peisistratos in 540 B.C. but it gradually developed into a proper domination lasting - with short intervals - until the end of the 4th century B.C., when Delos was finally declared free and independent (314 B.C.). The independence of the island lasted until 166 B.C. when the Romans gave it over to the Athenians.
The Delian League in turn kept its treasury on Delos making it a rather wealthy location. They also passed several decrees, including that no one could be born or die on the island. Pregnant women were quickly shipped off to neighboring islands as was anyone who became ill.