Defensive tactics: The Greeks used a variety of defensive tactics to slow the Persian advance. They built a wall across the pass, and used their spears and shields to form a phalanx that the Persians could not break through. They also used their superior knowledge of the terrain to their advantage, ambushing the Persians and launching surprise attacks.
Leadership: The Greeks were led by a skilled and experienced commander, Leonidas I of Sparta. Leonidas was a charismatic and inspiring leader who motivated his men to fight to the death. He also made wise strategic decisions, such as choosing to fight at Thermopylae instead of in the open field.
Persian overconfidence: The Persians were overconfident and underestimated the Greeks. They believed that their superior numbers would easily overwhelm the Greeks, and did not take the necessary precautions to prepare for battle. This overconfidence led to several mistakes, such as sending a small detachment of soldiers against the Greeks at Thermopylae.
Greek determination: The Greeks were determined to defend their homeland against the Persian invasion. They were willing to fight to the death to protect their families and their way of life. This determination was a key factor in their victory at Thermopylae.