narrow valley between the southern Olympus and northern Ossa massifs of northeastern Thessaly, Greece. The valley is lined by cliffs that rise to 1,650 feet (500 m) on the south; in places it is only 90 to 165 feet (25 to 50 m) wide, and it is only about 6 miles (10 km) long. The Piniós River flows through the valley before emptying into the Aegean Sea. Legends attribute the glen's formation to both an earthquake and cleaving by the trident of the sea god, Poseidon; geologists believe the grassy defile or gorge to be a fracture ravine carved by local stream action. It was formed in the Quaternary Period (1.6 million years ago to the present) when the valley's stream eroded back sufficiently to provide an outlet for the Larissian Lake, which dammed up the Piniós River. The lake drained away through the vale's stream, which became the lower course of the Piniós River.

Inspired by the lushness of its vegetation, the ancient Greeks dedicated Tempe to the cult of Apollo, who, legend says, purified himself in the waters of the Piniós after killing the serpent Python. A temple was built in a recess on the right bank, and every eighth year a procession came from Delphi to gather sacred laurels awarded to the victors of contests.

Because it provides access from the coast of Macedonian Greece to the Thessalian plain, the vale has been a traditional invasion route. Known to the Byzantines as Lykóstomo (“Wolf's Mouth”), it was called Boğaz (“Gorge”) by the Turks. The ruins of castles and fortifications extending from the Roman period to the Middle Ages mark strong points of Tempe, which the Greeks attempted to defend in 1941 during the German invasion.