Due to its privileged location, its marble and fishing, Iassos had been inhabited since the earliest days of the history. The city was founded by the Greek colonist coming from Argos nearly 9th BC and then inhabited by the immigrants from Miletus. However, Italian archaeologists under the directorate of Doro Levi have found Minoan houses and Mycenaean pottery which indicates that the site had been inhabited at much earlier date than arrival of Greeks.

The digs started 1960s reveled that oldest part of Iassos was on the top of Acropolis hill, now taken by the Byzantine fortress. These evidences show some similarities between the Crete, Greece and Anatolian cultures. The chief divinities of Iassos were Apollo and Artemis. One of the inscriptions discovered in Iasos mentions Artemis Astias, apparently mixture of old Carian deity Goddess with Artemis the hunter. Her temple had unroofed cella. On the other side, theatre and festivals arranged for Dionysus shows also importance of God Dionysus in Iasos. The city is mainly is situated on the rocky island with the exception of city walls and necropolis.

One of the very impressive monuments of Iasos is a monumental mausoleum, a temple tomb in Syrian style. The burial chamber is surmounted by small Corinthian temple which rested on 10 stepped crepidoma. Although it is dated to Roman Period and many skeletons were discovered in the tomb, we have no idea about the identities of the owners. Behind the village, there are extensive ruins of a defense wall dating to 4th century BC. Rectangular in shape and situated at a certain distance from the town, this wall is believed to be used by a garrison protecting the city.

Among the noteworthy monuments, we can mention partly excavated agora; well preserved Odeon dated to Roman Imperial Period; Ceasarium where main deities of the city were worshipped; ruins of a Roman theatre dedicated to Dionysus and to the people of Iasos; a Roman villa where Italian team discovered the remains of Roman Mosaics and frescoes; a shrine dedicated to Demeter and Kore.

Some of the coins discovered at Iassos show the Dolphin and a young boy. This reminds us the story of a young boy who was befriended by a dolphin, a story both mentioned by Plinius and Aelian. According to Plinius, Alexander the Great was so charmed with the story of Dolphin and young boy, he took the youth along with him on his campaign to Asia and made the boy the head of priesthood of Poseidon, the god of Sea.