Letoon or Letoum, was a sanctuary of Leto near the ancient city Xanthos in Lycia in modern Muğla Province, Turkey. Archaeological finds at the site, which was never a fully occupied settlement, but remained essentially a religious center, date back to the late sixth century BC, before the Greek cultural hegemony in Lycia, which began in the early fourth century BC. Letoon was inscribed as a UNESCO World Heritage Site in 1988, along with Xanthos.