Makronisos (, lit. Long Island), or Makronisi, is an island in the Aegean Sea, in Greece, notorious as the site of a political prison from the 1920s to the 1970s. It is located close to the coast of Attica, facing the port of Lavrio. The island has an elongated shape, north to south and east to west at its widest point, and its terrain is arid and rocky. It is the largest uninhabited Greek island.
It is part of the Kea-Kythnos regional unit and in the municipality of Kea.
History
In ancient times the island was called Helen (). It protected the ancient harbours of Thorikos and Sounion. It was also called Macris (Μάκρις), from its length. Strabo describes it as 60 stadia (9.4 km) in length; but its real length is seven geographical miles (12 km). It was uninhabited in antiquity, as it is at the present day; and it was probably only used then for the pasture of cattle. Both Strabo and Pausanias derive its name from Helen of Troy, the wife of Menelaus: the latter writer supposes that it was so called because Helen landed here after the capture of Troy; but Strabo identifies it with the Homeric Cranae, to which Paris fled with Helen, and supposes that its name was hence changed into Helena. There cannot, however, be any doubt that the Homeric Cranaë was opposite Gythium in Laconia.
The Kea Channel between Makronisos and neighbouring Kea was the site of the sinking, in 1916, of HMHS Britannic, sister ship of the RMS Titanic.left|thumb|243x243px|1924 photograph of MakronissosAfter the Burning of Smyrna in 1922 and the population exchange between Greece and Turkey, Greek refugees from the Ottoman Empire were transferred to Makronisos, where a quarantine station (to minimize the spread of smallpox and typhus infection) was established. Between 1922 and 1923, 12,295 refugees, mostly women, children, and the elderly, passed through Makronisos.