King Leonidas was the king of the ascetic tribe of Sparta during the 5th century B.C. The people were bound by Spartan law. New born males of the tribe were meticulously inspected by Spartan elders for adequate size requirements & unwanted birth defects. Those who failed the inspection were left to die in the wilderness.
Young Sparta boys were made to survive on their own tidings in the wilderness until they came back to Sparta as fierce warriors. Based on the situation alone, it was surprising that Sparta was able to possess more than three hundred soldiers at all. The tribe's infatuation of producing the perfect warriors did not stop for the young men of Sparta until they reached 30 years of age & served in the Spartan army for another thirty to forty years. The Spartan Law made them very much a war loving tribe that hardly rejected any call to war.
The Spartans fighting specialty was as a single impenetrable unit, forward thrusting, one way & notably elite assault unit. They were documented as a fearsome & formidable army, made stronger by their laws for which forbids them to neither retreat nor surrender. Suicidal tendency is prevalent within such a school of thought.
The Spartan military strength is within their formations, shield, spear, & compounded strength. The semi nakedness suggested extensive use of their large shields to protect their bodies. In true history, the warriors may have actually worn frontal upper body armor instead of being bare-chested as in the recent movie 300.
King Leonidas & his three hundred Spartans were made famous by battling the Persian army led by King Xerxes, at the pass of Thermopylae, in 480 B.C. during the Persian Wars. According to Herodotus; a Dorian Greek historian who lived in the 5th century BC, Leonidas had been warned by the Delphic oracle that either Sparta would be destroyed or their king would lose his life.
The King Leonidas were winning every battle against the Persians whom were desperate to find a way into Greek other than facing the Spartans. However, a greek traitor named Ephialtes led the Persians through an alternative route to surround King Leonidas & his men. The three hundred Spartans were eventually slaughtered by the massive Persian army & the Persians mangled the corpse of King Leonidas.
The Spartan principle of "No retreat & no surrender" got the best of the ego induced chiseled physique heroes of Sparta. Spartans were expected to fight beyond reason & perceived death in battle as the highest honor a man could ever achieve in a lifetime.