Mythology has it that the three giants Phoebos, Kinnas and Kios fled to this island after they had been defeated at the great battle of the gods and the Titans. Heracles supposedly stayed here for a while after he had performed his 12 labors. His ship had sunk on his way home, and he managed to swim to Kos, where he met the angry shepherd Andagoras whom he fought for many hours. He then sought refuge in the mountains since king Eurypilos had ordered his arrest, but managed to capture the king`s daughter Chalkiope, with whom he had Thessalos, future king Of Leros and Nissyros.

The king of the Carians led his people to the island sometime in the 2nd Millennium BC, and this people from Asia Minor are traditionally considered to have been one of the first settlers on this island. They were succeeded by the Minoans, Cretans, and then, in the 10th century BC, the Dorians arrived. At this time, the island was called Meropida.

The people of Kos were forced to join the Persian forces against Greece in the 5th century BC, but that changed after the Persians were defeated at the battle of Salamis. After that, Kos was a full member of the Delian League and the island was prospering under its democratic constitution.

From an early stage, the god of medicine, Asclepius, was worshipped here, and pilgrims from all over came to his temple to go through cleansing rituals, sleep in the temple, and be cured. It is no coincidence that the father of medicine, Hippocrates, was born here.

In the 4th century BC Kos joined sides with the Macedonians, and the Romans conquered the island in the 2nd century BC. St. Paul the Apostle visited the island on one of his missions, and some of the earliest churches of Greece were built here - you can still see the ruins of a couple of them. Unfortunately most ancient and Christian buildings were destroyed in a big earthquake in AD 535.

With the exception of many pirate raids, Kos flourished during the Byzantine era . The Genuans and Venetians ruled the island in the 12th century, but it came under the command of the Knights of Rhodes in 1315, who taxed the locals heavily.

The Turks occupied the island in 1522, and massacres and harsh treatment of the people followed. Kos was given to Italy in 1912, and freed in 1948.