Kythnos or Thermia, located between Gia and Serifos, is 52 nautical miles from Piraeus, a distance that normal ships cross in 3 hours and from the port of Lavrio in only 2 hours. It has an area of ​​99 square meters. kilometers and approximately 1,500 permanent residents. It probably took its name from its founder Kythnos, although his historical existence is very doubtful. The word (Dryopian or Phoenician) may still be based on the root "kyth" which comes from the verb "keutho" meaning to hide (keithmon: dark, deep place where one disappears). This interpretation of the name refers to some physical property of the island during early antiquity (shaded forests, deep valleys or caves or even mining).
According to the archaeological and anthropological findings, it was already inhabited since the 8th millennium BC. Recent palaeontological discoveries at the site of Maroulas, near today's Loutra, have found traces of four tombs from the Mesolithic Period, evidence that proves that there was perhaps the earliest human settlement in the Cyclades. The existence of around twenty circular slate structures in the Skouries area enclosing metallurgical furnaces as well as a copper mining mine at Cape Tzouli, belonging to the Proto-Cycladic period, have also been recorded. The first inhabitants were probably Greek Pelasgians and in Median times they were Dryopes. The Cyclopean walls and the temples they left behind are remarkable. After the Dryopes, the island was settled by Iones. Later Aristotle refers to the Cythnian State and considers it ideal. In the Roman era, the island was part of the province of Achaia, and then the Byzantines included it in the "Theme of the Aegean". In 1207 AD the Frankish rule is imposed here as well by the Venetian nobleman Marco Sanudo. In 1292 AD, Thermia (as the island began to be called in the Middle Ages because of the springs that gushed out "warm" waters) was plundered by the admiral of Aragon and in 1537 it was occupied by the Russians, while in 1827 the island again acquired the its ancient name - Kythnos - and participates in the liberation struggle against the Turks. In 1862, the rebels who came from Syros on the ship "Karteria" and the military forces that had remained loyal to Othon and who had arrived here on the ship "Amalia" clashed in the bay of Loutra. During the clashes, the "royalists" prevailed over their opponents, as a result of which the fighters Leotsakos, Maraitini and Skarvelis were killed. These events took their place in modern modern Greek history and were called "Kythniaka". Today, in the bay of Agia Irini, next to the Baths, an unnecessary marble plaque with their names reminds of these first fighters of democracy in our country.

Source: DAFNI - Network of Sustainable Islands of the Aegean
http://www.dafni.net.gr/