The Dorians invaded it in the 11th century BC, establishing a Dorian colony with a large contingent of settlers from Epidaurus, whose Asclepius cult made their new home famous for its sanatoria. The other chief sources of the island’s wealth lay in its wines and, in later days, in its silk manufacture.s early history–as part of the religious-political amphictyony that included Lindos, Kamiros, Ialysos, Cnidus and Halicarnassus, the Dorian Hexapolis (hexapolis means six cities in Greek),–is obscure. At the end of the 6th century, Kos fell under Achaemenid domination but rebelled after the Greek victory at the Battle of Mycale in 479. During the Greco-Persian Wars, before it twice expelled the Persians, it was ruled by Persian-appointed tyrants, but as a rule it seems to have been under oligarchic government. In the 5th century, it joined the Delian League, and, after the revolt of Rhodes, it served as the chief Athenian station in the south-eastern Aegean (411–407). In 366 BC, a democracy was instituted. In 366 BC, the capital was transferred from Astypalaia to the newly built town of Kos, laid out in a Hippodamian grid. After helping to weaken Athenian power, in the Social War (357-355 BC), it fell for a few years to the king Mausolus of Caria.Proximity to the east gave the island first access to imported silk thread. Aristotle mentions silk weaving conducted by the women of the island. Silk production of garments was conducted in large factories by women slaves.

In the Hellenistic age, Kos attained the zenith of its prosperity. Its alliance was valued by the kings of Egypt, who used it as a naval outpost to oversee the Aegean. As a seat of learning, it arose as a provincial branch of the museum of Alexandria, and became a favorite resort for the education of the princes of the Ptolemaic dynasty. During the hellenistic age, there was a medical school; however, the theory that this school was founded by Hippocrates (see below) during the classical age is an unwarranted extrapolation. Among its most famous sons were the physician Hippocrates, the painter Apelles, the poets Philitas and, perhaps, Theocritus. Diodorus Siculus (xv. 76) and Strabo (xiv. 657) describe it as a well-fortified port. Its position gave it a high importance in Aegean trade; while the island itself was rich in wines of considerable fame. Under Alexander the Great and the Egyptian Ptolemies the town developed into one of the great centers in the Aegean; Josephus quotes Strabo to the effect that Mithridates was sent to Kos to fetch the gold deposited there by the queen Cleopatra of Egypt. Herod is said to have provided an annual stipend for the benefit of prize-winners in the athletic games, and a statue was erected there to his son Herod the Tetrarch (“C. I. G.” 2502 ).

In a distance 3.5 kilom. northwest of Kos town, at the slopes of a low mount with a view at the coasts of Asia Minor, there is the monumental complex of Asclepio. The space was located in the beginnings of 20th century by the German archaeologist R. Herzog and the research continued later Italian archeologists who attempted, and the restoration of the monument projecting mainly to the Roman side. The complex is extended in three mounds. At the lowest a gallery at Π shape (3rd century b. C) that today is maintained in level of foundation, it encompassed the space from the north, east and west side. In the middle of the north side through a propylon was the access in the holy space by a scale. East of the gallery is preserved a complex of Roman thermals (3rd century b. C). West of the ascent scale towards the second mound there is in a Roman alcove in a little temple form statue base, oblation of the Kos Doctor Gaiou Stertiniou Xenofontos. In the middle mound are remains of the altar of Asclepius (4th century b. C) and opposite the mound is saved the Ionic temple of Asclepius. South of the temple it was the untrodden, where the patients Kos Island – Asclepion Archeological war laying waiting for God’s Help. South of the untrodden there is the entrance of the holly source. East of the altar is placed a small Corinthian temple (2nd century. AD) dedicated, probably, in Apollo. At the third and upper mound dominates the big Dorian temple of Asclepius (2nd century b. C), copy of the corresponding in Epidaurus.