According to Greek mythology, Apollo was born on this tiny island in the Cyclades archipelago. Apollo's sanctuary attracted pilgrims from all over Greece and Delos was a prosperous trading port. The island bears traces of the succeeding civilizations in the Aegean world, from the 3rd millennium B.C. to the palaeochristian era. The archaeological site is exceptionally extensive and rich and conveys the image of a great cosmopolitan Mediterranean port.

Źródło: World Heritage Convention
http://whc.unesco.org/en/list/530