Ancient Greeks were more than resourceful and they always had their special way to interpret everything! So, the myth says that the island of Delos was once a rock which aimlessly roamed the seas. In fact, its name at the time was not even Delos, but Asteria or Ortygia.
This rock (Delos) would continue to wander the seas if it was not for an agreement that took place between Zeus and Poseidon, in order to provide Leto with a place to live and to give birth to her twins. The Gods Apollo and Artemis!
Leto was a beautiful Titan that Zeus fell in love with. Something that resulted to Hera being so annoyed that she had ordered everyone not to accept Leto anywhere.
Poseidon, the god of the sea caught this “rock” and placed it in the middle of the Cyclades so it would be protected from all sides, securing it firmly with chains. That rock became a normal island. The island of Delos.
At Delos arrived Leto and gave birth to Artemis and Apollo.
To Apollo as we all know are attributed qualities that no one else ever had. He was the god of light, music and divination!
The Temple of Apollo on Delos along with the one later constructed in Delphi were meeting points for all ancient Greeks and although Delos was inhabited since 2500 BC, the love for Apollo is what made it the sacred island of all Ancient Greece.
On Delos though there were built temples not only for Apollo but also for many other deities even non-Greek ones. And often great celebrations were organized where all the city-states of the time would participate and would bring to the gods rich offerings.