Thessaly is a region in northern Greece. The term refers narrowly to the area of two great plains drained by the Peneios River but is also used to designate a much broader region, which extends from Mount Olympos in the north to Mount Oita in the south. In the Archaic and Classical periods there were at least twenty-five Thessalian poleis; the most important of them were Larissa, Pharsalos, and Pherai.