During the 5th century BC, the Persians were out to conquer the world, including the powerful city-states of Greece. It started under Darius the Great, who is mentioned in the Old Testament books of Ezra and Nehemiah. After the death of Darius in 486 BC, his son, Xerxes, took over world-conquering duties. Xerxes is the Persian king mentioned in the Old Testament Book of Esther.
In 480 BC, the Persians, under Xerxes, pursued a great military campaign against Greece. The famous pass at Thermopylae was the only land route the Persians could take to attack the lower city-states. Because of the narrow nature of the pass, this is where the Spartans and their allies set up their defense.
Legend has it that 300 Spartans held off roughly a million Persians. However, that’s not exactly what happened. In reality, there were 300 elite Spartan bodyguards that served King Leonidas, but there were a number of Greek allies that also joined the fight. A good estimate is about 7,000 soldiers from 14 different Greek city-states.
The Persian side was huge, but it was short of a million. Most modern scholars suggest a Persian army of 100,000 to 300,000. These were still not great odds for the much smaller Greek alliance.
In any event, there was a three-day battle where the Greeks held off the Persians with legendary feats of courage. The Persian army was primarily archers with wicker shields, which is one of the reasons the Spartans were able to hold out as long as they did. The Persian arrows couldn’t penetrate the metal of the overlapped hoplite shields.
On the third day of the battle, it was obvious that the Persians would overwhelm the outnumbered Greeks. So Leonidas pushed his elite Spartans into the widest part of the pass in order to inflict maximum Persian casualties and give the remaining Greek soldiers an avenue of escape. In the ensuing clash, Leonidas was killed in heroic fashion. His men fought furiously to retrieve his body, but were unsuccessful.
The Battle of Thermopylae and the role of the 300 Spartans soon acquired legendary status. Free men had sacrificed themselves in order to defend the Greek way of life against foreign invasion.