Thessaly, the largest division of ancient Greece, a wide, fertile plain stretching southward from the Macedonian border to the Maliac Gulf, and entirely surrounded by mountains save the Vale of Tempe in the NE. between Mounts Ossa and Olympus; was conquered by Philip of Macedon in the 4th century B.C., and subsequently incorporated in the Roman Empire, on the break up of which it fell into the hands of the Venetians, and eventually of the Turks (1335), and remained a portion of the Ottoman Empire till 1881, when the greater and most fertile part was ceded to Greece. Chief town, Larissa.