Battle of Thermopylae

The weak point in the defense was the mountain path that could be taken around the Thermopylae isthmus.

An excerpt from the article 31 facts about Battle of Thermopylae

Leonidas knew that there was a path through the oak-covered slopes of the gorge that could be used to get around the defender’s positions. The Persians could not have known this path and the King of Sparta hoped that they would not discover it. However, as a precaution, he sent Phocians (1000 hoplites) there to undertake the defense of the path-they were to kill any scouts.