What is possibly the earliest known Mesolithic settlement in the Cyclades, dated by laboratory analyses to the 9th or 8th millennium bc, has been identified on the coast at Maroulas (500m north of Loutra) on Kythnos. The presence of metal ores on the island have also meant that Kythnos played an important role in the development of early metallurgy during the 3rd millennium bc: a number of copper-smelting furnaces have been identified by archaeologists at Skouries near the eastern extremity of the island. The presence of the metallurgic activity may also have given rise in Classical/Hellenistic times to the island’s several towers; unlike those on Siphnos, however, few of them are well-preserved. The naturally fortified summit at Kastro tis Orias—later the Byzantine capital of the is land—may also have seen Mycenaean settlement.
Herodotus says that Kythnos was originally settled by Dryopes—colonisers, perhaps from Styra on Euboea, whither they had come when they left the mainland of Greece; later on, Ionian settlers arrived on the island. The ancient city of Kythnos was at Vryokastro, overlook a complex of inlets in the middle of the west coast. It appears to have been continually inhabited from the 10th century bc to the 7th century ad, and has yielded rich archaeological finds. Kythnos supplied two ships to the Greek fleet at Salamis. It was a member of the Delian League and became tributary to Athens. Aristotle appears to have praised Kythnos in his (now lost) essay, The Constitution of Kythnos.
After the death of Nero in 68 ad, an imposter claim to be the emperor was driven ashore at Kythnos in a storm; he was seized and put to death by Calpurnius As prenas, the proconsul of Galba. Pliny noted that the is land produced excellent cheese, a tradition which is maintained today.
With increasing piracy and insecurity of the coasts, the main settlement at Vryokastro was abandoned in the 6th/7th century ad in favour of the impregnable site of Kastro tis Orias on the rugged northwest coast. This remained the capital during the periods of Byzantine and Latin rule, during which time the island was known as Thermia, from its renowned hot springs at Loutra. In 1207 the island came under the rule of the Venetian overlord of Naxos , Marco Sanudo, nephew of Doge Enrico Dandolo, and became one of the seventeen islands of the ‘Duchy of the Archipelago’. In 1336 Niccolo Sanudo gave the barony of Kythnos to the Gozzadini family of Bologna, who held onto the island for some time after the capitulation of the larger members of the archipelago to the Turks.
The early 1600s saw the migration of the population from the coast al stronghold of Kastro to the centre of the island where the new settlement of Chora was established with many fine churches. In 1617 the island finally fell to the Turks. In 1823 the population was decimated by plague. The island became a place of exile for political prisoners under the increasingly autocratic rule of Greece’s first King, Otho, and an unsuccessful expedition was mounted by rebels from Syros to free them in 1862. The industrial prospecting for iron-ore altered the traditionally agricultural economy of the island in the mid 19th century; the yield was less than expected and the mines were closed at the beginning of the Second World War.
Kythnos Island is part of the Cyclades Island Group, Greece.