The Battle of Thermopylae (/θərˈmɒpɪliː/ thər-MOP-i-lee)[14] was fought in 480 BC between the Achaemenid Persian Empire under Xerxes I and an alliance of Greek city-states led by Sparta under Leonidas I.

By 480 BC, a decade after the Persian defeat at Marathon, Xerxes had amassed a massive land and naval force, and subsequently set out to conquer all of Greece.

They arrived at Thermopylae by late August or early September; the outnumbered Greeks held them off for seven days (including three of direct battle) before their rear-guard was annihilated in one of history's most famous last stands.

Subsequently, Leonidas, aware that his force was being outflanked by the Persians, dismissed the bulk of the Greek army and remained to guard their retreat along with 300 Spartans and 700 Thespians.

Wary of being trapped in Europe, Xerxes withdrew with much of his army to Asia, reportedly losing many of his troops to starvation and disease while also leaving behind the Persian military commander Mardonius to continue the Achaemenid Empire's Greek campaign.

[16] These wars are also described in less detail by a number of other ancient historians including Plutarch, Ctesias of Cnidus, and are referred to by other authors, as by Aeschylus in The Persians.

[29] A preliminary expedition under Mardonius in 492 BC secured the lands approaching Greece, re-conquered Thrace, and forced Macedon to become a client kingdom of Persia.

[35] At this, Darius began raising a huge new army with which to completely subjugate Greece; however, in 486 BC, his Egyptian province revolted, indefinitely postponing any Greek expedition.

[37] Xerxes directed that the Hellespont be bridged to allow his army to cross to Europe, and that a canal be dug across the isthmus of Mount Athos (cutting short the route where a Persian fleet had been destroyed in 492 BC).

[54] Leonidas chose to camp at, and defend, the "middle gate", the narrowest part of the pass of Thermopylae, where the Phocians had built a defensive wall some time before.

[58] According to Plutarch, when one of the soldiers complained that, "Because of the arrows of the barbarians it is impossible to see the sun", Leonidas replied, "Won't it be nice, then, if we shall have shade in which to fight them?

[68][69][b] These estimates usually come from studying the logistical capabilities of the Persians in that era, the sustainability of their respective bases of operations, and the overall manpower constraints affecting them.

Furthermore, the numbers changed later on in the battle when most of the army retreated and only approximately 3,000 men remained (300 Spartans, 700 Thespians, 400 Thebans, possibly up to 900 helots, and 1,000 Phocians stationed above the pass, less the casualties sustained in the previous days).

The pure ruggedness of this area is caused by torrential downpours for four months of the year, combined with an intense summer season of scorching heat that cracks the ground.

With the sea on one side and steep, impassable hills on the other, King Leonidas and his men chose the perfect topographical position to battle the Persian invaders.

Recent core samples indicate that the pass was only 100 metres (330 ft) wide, and the waters came up to the gates: "Little do the visitors realize that the battle took place across the road from the monument.

"[87] The pass still is a natural defensive position to modern armies, and British Commonwealth forces in World War II made a defence in 1941 against the Nazi invasion mere metres from the original battlefield.

[8] Later that day, however, as Xerxes was pondering what to do next, he received a windfall; a Trachinian named Ephialtes informed him of the mountain path around Thermopylae and offered to guide the Persian army.

The simultaneous naval Battle of Artemisium had been a tactical stalemate, and the Greek navy was able to retreat in good order to the Saronic Gulf, where it helped to ferry the remaining Athenian citizens to the island of Salamis.

The battle itself had shown that even when heavily outnumbered, the Greeks could put up an effective fight against the Persians, and the defeat at Thermopylae had turned Leonidas and the men under his command into martyrs.

[137] Alternatively, the argument is sometimes advanced that the last stand at Thermopylae was a successful delaying action that gave the Greek navy time to prepare for the Battle of Salamis.

[136] Far from labelling Thermopylae as a Pyrrhic victory, modern academic treatises on the Greco-Persian Wars tend to emphasise the success of Xerxes in breaching the formidable Greek position and the subsequent conquest of the majority of Greece.

[142] A second reason is the example it set of free men, fighting for their country and their freedom: So almost immediately, contemporary Greeks saw Thermopylae as a critical moral and culture lesson.

A well-known epigram, usually attributed to Simonides, was engraved as an epitaph on a commemorative stone placed on top of the burial mound of the Spartans at Thermopylae.

[147] It was well known in ancient Greece that all the Spartans who had been sent to Thermopylae had been killed there (with the exception of Aristodemus and Pantites), and the epitaph exploits the conceit that there was nobody left to bring the news of their deeds back to Sparta.

The first line of the epigram was used as the title of the short story "Stranger, Bear Word to the Spartans We…" by German Nobel Prize laureate Heinrich Böll.

John Ruskin expressed the importance of this ideal to Western civilization as follows:Also obedience in its highest form is not obedience to a constant and compulsory law, but a persuaded or voluntary yielded obedience to an issued command ... His name who leads the armies of Heaven is "Faithful and True"... and all deeds which are done in alliance with these armies ... are essentially deeds of faith, which therefore ... is at once the source and the substance of all known deed, rightly so called ... as set forth in the last word of the noblest group of words ever, so far as I know, uttered by simple man concerning his practice, being the final testimony of the leaders of a great practical nation ... [the epitaph in Greek][161]Cicero recorded a Latin variation in his Tusculanae Disputationes (1.42.101): Additionally, there is a modern monument at the site, called the "Leonidas Monument" by Vassos Falireas, in honour of the Spartan king.

Leonidas answered: "If you had any knowledge of the noble things of life, you would refrain from coveting others' possessions; but for me to die for Greece is better than to be the sole ruler over the people of my race.

Herodotus writes that when Dienekes, a Spartan soldier, was informed that Persian arrows would be so numerous as "to block out the sun", he retorted, "So much the better...then we shall fight our battle in the shade.

[174] Here, on Alexander the Great's campaign against Persia in 330 BC, he faced the same situation, encountering a last stand of the Persian forces, commanded by Ariobarzanes, at a narrow pass near Persepolis who held the invaders for a month, until the enemy found a path to their rear.