Battle of Thermopylae

At the head of the Greek army was Leonidas and his 300 bravest hoplites.

An excerpt from the article 31 facts about Battle of Thermopylae

According to Herodotus, in selecting the 300 warriors, Leonidas paid attention to their degree of mastery of the craft of war, but also to the fact that each of them had a living male descendant. The Spartans were aware of the vast numerical superiority of the Persians and reckoned that many of them would be killed.