Leonidas brought 300 Spartans to Thermopylae. These men were selected from the Spartan king’s royal bodyguard, known as the Hippeis, and were sent in 480 BC during the Persian invasion led by Xerxes I.
The famous “300 Spartans” were only part of Leonidas’s force. The Greek army initially numbered roughly 7,000 soldiers, including contingents from Thespiae, Thebes, Phocis, and other city-states. The 300 were full Spartan citizens, or Spartiates, and tradition says Leonidas chose men who had living sons so their families would not be left without heirs.
After the Persians found a mountain route around the pass, Leonidas dismissed most of the Greek army. The 300 Spartans remained with approximately 700 Thespians and other defenders for the final stand. A common misconception is that only 300 Greeks fought at Thermopylae; the number refers specifically to Leonidas’s Spartan contingent.