The island is a part of the core of an ancient volcano, which erupted c.1640–1620 bc (perhaps a century earlier), destroying the Minoan civilizations of Thíra and, it is thought, neighbouring Crete. A large part of Thíra became submerged, and has remained so to this day.
In antiquity, the island was not especially famous for its wine, but this was to change in the Middle Ages. It belonged to the Byzantine empire until the crusaders sacked Constantinople in 1203–4 and Santorini was given to one of the Venetian conquerors, remaining in his family until 1336. It then became part of the duchy of Naxos but venice retained a strong influence; 1479–89 was another period of direct Venetian rule. It was Venetian enterprise that made Santorini an important wine producer. The wine it exported was made from a mixture of grapes, chiefly the white athiri and red mandilaria, and it was prized for its sweetness and high alcohol which enabled it to withstand the six-month sea voyage, via Venice, to western Europe. Santorini was conquered by the Ottoman Turks in 1579, but the Turks did not discourage the production of the only cash crop that the island’s volcanic soil could sustain.