Why is Thermopylae called the Hot Gates?

Short answer

Thermos means hot and pylai means gates. The pass had hot springs at the foot of its cliffs, and it was a narrow gateway into central Greece. Both come from the same geological fault.

The narrow pass of Thermopylae between cliffs and sea in 480 BC — Reconstruction of the pass in 480 BC: the road squeezed between Mount Kallidromo and the sea. Today the coast lies kilometres further north.

The gates

A fault line runs along the foot of Mount Kallidromo. The land on one side dropped and was flooded by the sea; the other side stayed up as a steep cliff. Between the two ran a strip of shore just wide enough for a road. Herodotus says that at points it was only wide enough for a single cart.

The heat

The same fault is also a pipe for hot water. Herodotus mentions the springs and an altar of Heracles beside them; the locals called them “the Pots”.

Untangled History · how a hot spring works

01 Rain soaks in Rain on Mount Kallidromo seeps down through cracks in the rock.

02 It heats up The deeper it goes, the hotter the rock: roughly 25–30 °C more per kilometre.

03 It rises Hot water is lighter, so it climbs back up along the fault.

04 Hot gates It comes out at the foot of the cliff, right beside the narrow road.

The gates are gone, the heat is not

Since 480 BC the Spercheios river has filled the gulf with mud, and the coast now lies kilometres away from the old road. The narrow gate has become a wide plain. The springs still flow, and they still smell of sulphur.