Tílos is a small Greek island and municipality located in the Aegean Sea. It is part of the Dodecanese group of islands, and lies midway between Kos and Rhodes. It has a population of 533 inhabitants (2001 census). Along with the uninhabited offshore islets of Antitilos and Gaidaros, it forms the Municipality of Tilos, which has a total land area of 64.525 km². Tilos is part of the Rhodes peripheral unit. Tílos has an inverted ‘S’ shape, is about 14.5 km long, north-west to south-east, with a maximum width of 8 km and an area of about 61 km². The island has a mountainous limestone interior, volcanic lowlands, pumice beds and red lava sand, like its north western neighbour Nisyros. It is well supplied by springs, and is potentially very fertile and productive. Its coasts are generally rocky or pebbled, but there are also a number of sandy beaches.
Popularly, Telos was the son of Helios and Halia, the sister of the Telchines. He came to the island in search of herbs to heal his ill mother, and later returned to found a temple to Apollo and Neptune. However, Telos (Telo or Tilo) does not appear in Greek mythology and the name probably has an unknown pre-Hellenic origin. Pliny the Elder notes that in antiquity Telos was known as Agathussa (also Agathusa and Agathousa). In the Middle Ages, it was known by the Italian Piscopi or Episcopi (also Pisconia).