Didyma (; ) was an ancient Greek sanctuary on the coast of Ionia. It contained a temple and oracle of Apollo, the Didymaion. In Greek didyma means "twin", but the Greeks who sought a "twin" at Didyma ignored the Carian origin of the name. Next to Delphi, Didyma was the most renowned oracle of the Hellenic world, first mentioned among the Greeks in the Homeric Hymn to Apollo. Its establishment preceded literacy and even the Hellenic colonization of Ionia. Mythic genealogies of the origins of the Branchidae line of priests, designed to capture the origins of Didyma as a Hellenic tradition, date to the Hellenistic period.