The significance of the Battle of Thermopylae in ancient history lies in its demonstration of courage and sacrifice against overwhelming odds. Fought in 480 BCE during the Greco-Persian Wars, it featured a small Greek force, led by King Leonidas of Sparta, facing the vast Persian army commanded by King Xerxes. Although the Greek forces were ultimately defeated, the battle became a symbol of resistance and determined valor, inspiring later generations. Thermopylae showcased the Greeks' commitment to freedom and showcased Spartan bravery, motivating the Greek city-states to unite against Persia, eventually leading to Greek victories at Salamis and Plataea.