The plain is formed by the Pineios River and its tributaries and is surrounded by mountains: the Pindus mountain range to the west, which separates Thessaly from Epirus; Mount Othrys and its outliers in the south; Mount Pelion to the east; Mount Ossa and Mount Olympus to the northeast, with the pass of the Tempe Valley leading to Macedonia; and the Chasia and Kamvounia mountains to the north.