Wikipedia has a good overview of the Battle of Thermopylae here.
It is 480 BC and the Persians under Xerxes I are marching with a huge army to invade Greece. Xerxes is eager to avenge the failure of his father Darius I’s invasion which was thwarted by the Greeks at the Battle of Marathon in 490 BC.
Unfortunately for the Spartans, the invasion comes during the sacred festival of Carneia as well as during the Olympic Games and so it would be doubly sacrilegious for them to go to war at this time. Therefore it is decided to send an advance force to hold the ‘hot gates’ until the main Spartan army can march and join them later. King Leonidas takes his personal royal bodyguard of 300 men and about 1,000 support troops and helots. They will later be joined by other small contingents of Greeks.
Leonidas and his men are under no illusions; they know they are going to their deaths. Even though the hot gates will afford them a narrow and advantageous defensive position, even though the Spartans are the Delta Force, the Royal Marines of the ancient world, the Persian army numbers in the hundreds of thousands. And the Oracle of Delphi has prophesied:
O ye men who dwell in the streets of broad Lacedaemon!
Either your glorious town shall be sacked by the children of Perseus,
Or, in exchange, must all through the whole Laconian country
Mourn for the loss of a king, descendant of great Heracles.
Thus we know that Leonidas is under no illusions and also by the fact that he gives orders that only those Spartans may come who have living sons. He asks for volunteers to replace those who do not. We also have the following from Plutarch:
And another saying, What, Leonidas, do you come to fight so great a number with so few? — he returned: If you esteem number, all Greece is not able to match a small part of that army; if courage, this number is sufficient.
And to another discoursing after the same manner he said, I have enough, since they are to be killed.
And when they again asked him whether he had any other enterprise in his thought, he replied, I pretend to go to hinder the barbarians’ passage, but really to die fighting for the Greeks.
The Spartans always esteemed courage and not numbers as this famous quote by King Agis II tells:
The Spartans do not ask how many but where they are.
The Spartans take up the defence of the hot gates by forming a shield wall or phalanx. At this time the Greek hoplites fought with a long spear so that only the first two ranks could fight the enemy. Later Philip of Macedon would introduce the 16 foot sarissa, a long pike, allowing the first five rows of the phalanx to fight. (When occasion demanded, they also fought with a short sword).
Over three days the Spartans ‘cut to ribbons’ all the Persian troops sent against them, including Xerxes elite troops, the notorious ‘Immortals’. Their name stemmed from the fact that they wore masks to conceal their individual identity and their numbers were always maintained at exactly 10,000 so that it seemed that none ever died.The Spartans are undone finally when the Persians learn from a Greek traitor that there exists a mountain path which will allow them to outflank and attack the Spartans from the rear. On learning that the path has not been held by the Phocian allies he had stationed there, Leonidas orders his Greek allies to retreat and prepares to form a rearguard with only his 300 Spartans, 700 Thespians and 400 Thebans. This will allow his other 3,000 Greek allies to escape.
Leonidas’ rearguard leave their defensive position and attack Xerxes’ advancing army so as to sell their lives dearly and kill as many Persians as they can.Two of Xerxes’ brothers are killed at this time as is Leonidas himself, thus fulfilling the Delphic prophecy. As the Immortals arrive in their rear the Spartans retreat to a hill where they are showered with arrows until all are killed.
The Battle of Thermopylae was a defeat for the Spartans. It did not significantly slow down the advance of Xerxes’ army, nor did it inflict significant losses on the Persians (although they lost some 20,000 men). But had the Persians not discovered the mountain pass, had the Spartans held the hot gates some days longer, Xerxes huge army would have run out of provisions and been forced to retreat. The defence of Thermopylae could have become a successful military operation instead of a courageous act of self-sacrifice.
The Battle of Thermopylae may have been a defeat, but as Michel de Montaigne said, ‘There are some defeats more triumphant than victories’. Thermopylae was a victory of the spirit, which takes no account of fear, no account of danger, no account of possible outcomes but which takes account only of the most important things: of honour, of duty and of freedom. As an example of courage, it may be equalled but it can never be surpassed.
Go tell the Spartans, stranger passing by, that here obedient to their laws we lie. Simonides of Ceos
Images from the movie '300' and Wikimedia