Iasos or Iassos was a city in Caria located on the Gulf of Iasos (now called the Gulf of Güllük), opposite the modern town of Güllük. It was originally on an island, but is now connected to the mainland.

Iassos dates back to 3000 BC. Once an island, has now joined the mainland and formed a peninsula. The remnants of three temples of Zeus, Apollo and Artemis remain along with numerous Roman buildings including an agora, theatre aquaducts, cisterns, gymnasium, baths and a bouleuterion. There is an open air museum with many artefacts on display. After some preliminary research done by Charles Texier starting in 1835, the site of the settlements in Iasos and the necropolis has been under regular and fully scientific excavations on behalf of the Italian School of Archaeology at Athens by Doro Levi Clelia Laviosa and Fede Berti .

The site of Iasos has been settled continuously since the Early Bronze Age, covering Geometric, Hellenistic and Roman periods, through the Byzantine period. In early times, Iasos was influenced by the culture of the Cyclades islands.

Today is is called Kiyikislacik and is famous of it abundant history, olive groves and cheap fish. It is an area of Turkey that remains untouched.

The site looks at the bay of Gulluk and is located in the Milas district of Muğla Province, Turkey, near the Alevi village of Kıyıkışlacık or Kıyı Kışlacık, about 31 km from the center of Milas and 20km from the airport.