Ancient historians consider Iasos a colonial foundation of Argos,but archaeology shows a much longer history. According to the ancient reports, the Argive colonists had sustained severe losses in a war with the native Carians, so they invited the son of Neleus, who had previously founded Miletus, to come to their assistance. The town appears on that occasion to have received additional settlers. The town, which appears to have occupied the whole of the little island, had only ten stadia in circumference; but it nevertheless acquired great wealth, from its fisheries and trade in fish. Iasos was a member of the Delian League and was involved in the Peloponnesian War (431–404 BC). After the Sicilian expedition of the Athenians, Iasos was attacked by the Spartans and their allies; it was governed at the time by Amorges, a Persian chief, who had revolted from Darius II. It was taken by the Spartans, who captured Amorges and delivered him up to Tissaphernes. The town itself was plundered on that occasion. It became part of the Hecatomnid satrapy in the 4th century and was conquered by Alexander. We afterwards find it besieged by Philip V, king of Macedon, who, however, was compelled by the Romans to restore it to Ptolemy V of Egypt. The mountains in the neighbourhood of Iasus furnished a beautiful kind of marble, of a blood-red and livid white colour, which was used by the ancients for ornamental purposes. Near the town was a sanctuary of Hestia, with a statue of the goddess, which, though standing in the open air, was believed never to be touched by the rain. The same story is related, by Strabo, of a temple of Artemis in the same neighbourhood. Iasus, as a celebrated fishing place, is alluded to by Athenaeus. The place is still existing, under the name of Askem or Asýn Kalessi. Chandler (Travels in As. Min. p. 226) relates that the island on which the town was built is now united to the mainland by a small isthmus. Part of the city walls still exist, and are of a regular, solid, and handsome structure. In the side of the rock a theatre with many rows of seats still remains, and several inscriptions and coins have been found there.
It seems to have been abandoned in about the 15th–16th century, in the Ottoman period, when a small town was founded nearby named Asin Kale or Asin Kurin, in the sanjak of Menteşe within the vilayet of İzmir.