Kasos, the southernmost island in the Dodecanese and the closest to Crete, is essentially the last link in the insular chain between Asia Minor and Crete.
The earliest traces of human habitation on the island date from the Final Neolithic/Early Bronze Age (4th and 3rd millennia BC). There are indications of permanent settlement, with strong Minoan influences, at the southwest end of the island, around the safe Khelastros bay, during the Middle and Late Bronze Age (until circa 1450 BC). In Mycenaean times the centre of activity was transferred to the north part of Kasos, to the naturally fortified site of Poli.
Homer, in Rhapsody II of the lliad, mentions Kasos as participating, along with other Dodecanesian islands, in the Trojan War.
In historical times the ancient capital, also called Kasos according to Strabo, remained in the area of Poli, arround the hill of the Mycenaean citadel. Potsherds scattered over the hilltop date from the Final Neolithic/Early Bronze Age to the Early Christian period and attest to the continuous occupation of the site, which together with the strip of land linking it with the harbour at Emboreio constituted the principal settlement core on the island over the centuries.
Kassians are mentioned for the first time in the Athenian Tribute lists of the 5th century BC, while the ethnic Kasos, written in Hellenistic inscriptions from beyond the bounds of the Rhodian state, point to the island’s independence in that period. Kassian emissaries (theoroi) are recorded on Delos in 275/4 BC and they are included in the list of independent cities, among which is Rhodes. Nonetheless, the presence of Late Hellenistic inscriptions with Rhodian deme-names indicates the eventual subjection of Kasos to the Rhodian state, which event must have taken place in the first half of the 2nd century BC. On present evidence, it seems that Kasos did not mint its own coinage but used the Rhodian. However, our knowledge of the history of Kasos during the period of incorporation into the Rhodian state, which is attested into Roman times, is limited.
During the Roman and Early Christian periods the main settlement on the island was apparently transferred to the coast around Emboreio bay, where there are traces of two Early Christian basilicas. Another two basilicas stood at Maritsa, to the east, while a fifth should be sought in the area of Panagia. The concentration of large public buildings of luxurious construction bears witness to the island’s prosperity in Early Christian times.
With the division of the Roman empire into provinces, in the reign of Diocletian (AD 284-305), Kasos was assigned to the XXVIII Provincia, the governor of which was based in Rhodes, to which the Episcopal Sees were subject too. With the division of the Byzantine state into Themata, however, Kasos was detached from the XVIII Thema of Kibyrrhaiotoi and included in the Thema of Crete. Information about the island in Byzantine and Medieval times is scant.
In 1207 the island was captured by the Venetians occupying Crete. In 1311 it was taken by the Knights of St John of Jerusalem, but following the intervention of the pope, Kasos and Karpathos were returned to the possession of Venice in 1315, so remaining until 1537, when they were conquered by the Ottomans. Suleiman the Magnificent granted the Kasians self-government, in return for an annual tax (maktu) of 1,000 grossi. Kasos is referred to as a deserted island by travellers in the 16th century. Nonetheless, it was repopulated, as borne out by patriarchal documents of 1622, mentioning that it was removed from the Archbishopric of Karpathos and became a patriarchal eparchy, which was ceded to the patriarchal official Hyaleas. The new settlements of Arvanitochori and St. Marina were built inland, because of fear of raids by pirates, who from before the Sack of Constantinople (1204) and for the ensuing five centuries were the scourge of the islands. Throughout the centuries life continued in the settlement around the acropolis of Poli.