Delos (modern Greek: Dhílos), the smallest, but historically one of the most important, of the Cyclades islands in the southern Aegean Sea. The area of the island is less than two square miles (5 km2). Greek legend makes Delos the birthplace of Apollo, and the island was a center of his worship. A famous temple of Apollo was here, and a festival was held every five years to honor him. The treasury of the Delian League, formed by Athens and other Greek states for protection against Persian aggression, was kept on Delos from 477 to 454 B.C. Delos became a busy trade center and slave market and Rome made it a free port in 166 B.C. After Mithridates VI of Pontus sacked Delos in 88 B.C., it never regained its prosperity and importance.