The fourth largest sanctuary in the Greek world after the Temple of Artemis (and the Heraion of Samos and the Olympieion at Sicily), the Sanctuary of Apolloion was built to rival the Artemision, employing one of the same architects, who was completing his work there, and having the same approximate dimensions.
The sanctuary was administered by the family of the Branchidae, who claimed descent from a purely eponymous Branchos, a youth beloved of Apollo. The priestess, seated above the sacred spring, gave utterances that were interpreted by the Branchidae. in the 6th century; the spring dried up, it was reported, and the archaic oracle was silenced. Though the sanctuaries of Delphi and Ephesus were swiftly rebuilt, Sanctuary of Apollo remained a ruin until the first steps of restoration were undertaken, in 334 BC. Inscriptions,
including inquiries and responses, and literary testimony record Sanctuary of Apollo's role as an oracle, with the "grim epilogue"of Apollo's supposed sanction of Diocletian's persecution of Christians, until the closing of the temples under Theodosius I. Sanctuary of Apollo was an ancient Ionian sanctuary containing a temple and oracle of Apollo, the Sanctuary of Apolloion. Next to Delphi, Sanctuary of Apollo was the most renowned oracle of the Hellenic world. With 122 columns, the Temple of Apollo is the second largest in the world, after Ephesus.