Final answer:
Thermopylae's narrow pass constrained the Persian army's numbers, providing a strategic location for the vastly outnumbered Greeks to delay the Persian advance, allowing for preparation of defenses and a Greek naval victory at Salamis.
Step-by-step explanation:
The Battle of Thermopylae was significant for the Greeks due to the geographic advantages the location provided. Thermopylae was a narrow pass between the mountains and the sea in northeastern Greece, which meant the Greeks could use the narrow terrain to their advantage.
This pass allowed a small Greek force, predominantly composed of Spartans led by King Leonidas, to hold off a much larger Persian army. The nature of the pass meant that the Persians could not utilize their vastly superior numbers or their cavalry effectively.
The delaying tactic at Thermopylae allowed other Greek city-states to prepare their defenses, particularly enabling the Athenian navy to subsequently achieve a crucial victory at the Battle of Salamis.