300 - Narrowest Passage at Thermopylae

This image depicts the "Black Buttocks" area of the Thermopylae pass.  According to Herodotus, who provides the history of the battle between the Greeks and Persians at Thermopylae, in 480 BCE, it is the narrowest point: 

This path ... stretches over the ridge of the mountain and ends ... by the stone called Black Buttocks ... where is the very narrowest part.

Credits

Quoted passage from Herodotus, Histories, 7.216

Image online, courtesy Livius.org