Leonidas (540-480 BC), also known as Leonidas the Brave was a Greek hero-king of Sparta, the 17th of the Agiad line, third son of Anaxandridas II of Sparta, who was believed to be a descendant of Heracles, possessing much of the latter’s strength and bravery. Leonidas is notable for his leadership at the Battle of Thermopylae.The Battle of Thermopylae was fought between an alliance of Greek city-states, led by King Leonidas of Sparta, and the Persian Empire of Xerxes I over the course of three days, during the second Persian invasion of Greece. It took place simultaneously with the naval battle at Artemisium, in August or September 480 BC, at the narrow coastal pass of Thermopylae. The Persian invasion was a delayed response to the defeat of the first Persian invasion of Greece, which had been ended by the Athenian victory at the Battle of Marathon in 490 BC. Xerxes had amassed a huge army and navy, and set out to conquer all of Greece. During two full days of battle the small force led by King Leonidas I of Sparta blocked the only road by which the massive Persian army could pass. After the second day of battle a local resident named Ephialtes betrayed the Greeks by revealing a small path that led behind the Greek lines. Leonidas, aware that his force was being outflanked, dismissed the bulk of the Greek army and remained to guard the rear with 300 Spartans, 700 Thespians, 400 Thebans and perhaps a few hundred others, most of whom were killed.Both ancient and modern writers have used the Battle of Thermopylae as an example of the power of a patriotic army defending native soil. The performance of the defenders at the battle of Thermopylae is also used as an example of the advantages of training, equipment, and good use of terrain as force multipliers and has become a symbol of courage against overwhelming odds.