King Xerxes I of Persia leads a vast army of soldiers into Europe to defeat the small city-states of Greece, not only to fulfill the idea of “one world ruled by one master”, but also to avenge the defeat of his father Darius I at the Battle of Marathon ten years before. Accompanying him are Artemisia, the Queen of Halicarnassus, who beguiles Xerxes with her charm, and Demaratus, an exiled king of Sparta, whose warnings Xerxes does not heed. Xerxes releases a captured Spartan soldier, Agathon, and tells him to inform the Greeks of their impending doom.

In Corinth, General Themistocles of Athens wins the support of the Greek city-states and convinces both their delegates and the Spartan representative, King Leonidas I, to grant Sparta leadership of the allied Greek forces, with Themistocles himself put in charge of the Athenian navy, recently reinforced with two hundred new ships. Outside the hall, Leonidas and Themistocles agree to fortify the narrow pass at Thermopylae with a vanguard force until the rest of the army arrives.

After learning of the Persian advance from Agathon, Leonidas travels to Sparta to rally the troops. In Sparta, his fellow king Leotychidas II is fighting a losing battle with the ephors – a council of five magistrates – over the religious harvest festival of Carneia that is due to take place, with members of the council arguing that the army should wait until the festival is over before marching to war, while Leotychidas fears that by that time the Persians may have conquered Greece. Leonidas decides to march north immediately with his personal bodyguard of 300 veteran men, who are exempt from the decisions of the ephors and the Gerousia, while Leotychidas remains in Sparta. The 300 Spartans are subsequently reinforced by a contingent of about 700 volunteer Thespians led by Demophilus, and a few other Greek allies.

After several days of fighting, Xerxes grows angry as his army is repeatedly routed by the Greeks, with the Spartans in the forefront. Leonidas receives word sent by his wife that, by decision of the Ephors, the remainder of the Spartan army, rather than joining him as he had expected, will only fortify the isthmus in the Peloponnese and will advance no further. The Greeks constantly beat back the Persians; following the defeat of most of his "Immortals" (personal bodyguard) by the Spartans and the death in battle of two of his brothers, Xerxes begins to consider withdrawing to Sardis until he can equip a larger force at a later date.

He prepares to withdraw, as advised by Artemesia (who, having a Greek mother, may have her own agenda to dissuade the king from continuing the invasion). Xerxes, however, receives word from the treacherous and avaricious Ephialtes, who has been also spurned by Spartan maiden Ellas (who accompanied her Spartan soldier boyfriend Phyllon to the battlefield, where he wishes to prove his courage), of a secret old goat-track through the mountains that will enable Persian forces to attack the Greeks from the rear. Promising to richly reward the traitorous goatherd for his betrayal (as Ephialtes had expected), an emboldened Xerxes sends his army onward. The Phocian troops dispatched by Leonidas to guard the secret path are summarily defeated.

Once Leonidas realizes he will be surrounded, he sends away the Greek allies to alert the cities to the south. Being too few to hold the pass, the Spartans instead attack the Persian front, where Xerxes is nearby. Leonidas is killed in the melée. Meanwhile, the Thespians, who had refused to leave, are overwhelmed (offscreen) while defending the rear. Surrounded, the surviving Spartans refuse Xerxes's demand to give up Leonidas' body in exchange for safe passage. They are then all annihilated as the remaining Immortals rain down a barrage of arrows.

After this, narration states that the Battle of Salamis and the Battle of Plataea end the Persian invasion, but that the Greeks could not have been organized and victorious without the time bought by the 300 Spartans who defied the tyranny of Xerxes at Thermopylae. One of the final images of the film is the stone memorial bearing the epigram of Simonides of Ceos, which the narrator recites in honor of the slain 300 Spartan men's bravery :

"Oh stranger, tell the Spartans that we lie here obedient to their word."

Then ends with "...But it was more than a victory for Greece, it was a stirring example to free people throughout the world of what a few brave men can accomplish once they refuse to submit to tyranny!"

The film's working title was Lion of Sparta.^[2]

The battle scenes were shot around Vouliagmenis Lagoon ^[4] (north of Loutraki and the Corinth Canal and west of the village of Perachora; northwest of Athens), not to be confused with the much smaller Lake Vouliagmeni, due south of Athens. The northern Corinthian site doubled as Thermopylae and the surrounding areas as it had become impossible to shoot at the actual location in Thermopylae. After 2,500 years of receding coastline, the strait where the actual battle was fought in 480 BC had converted into a broad coastal plain facing the Malian Gulf, adding about 3.5 kilometers of dry land to the coastline by the mid-20th century.

The Greek Defense Ministry made as many as 5,000 members of the Hellenic Army available for a pre-negotiated fee. However, budgetary constraints reduced the numbers to only two battalions (approximately 1,100 men). The largest establishing scenes of the Persian army entering Greece utilized many of these soldiers, together with a combined total of several hundred civilian extras, horses, cattle, ox carts and chariots. For the wider establishing scenes of the battle, one battalion was retained to play both Greeks (about 450 soldier extras) and Persians (about 650 soldiers). For closer compositions, military extras were employed by smaller units according to each day's shooting schedule. Director of photography Geoffrey Unsworth utilized tree groves, which lined the coastal plain aside the lagoon, to hide the obvious deficiency in the number of troops that would have been amassed on the Persian side of the battle line.^{[citation needed]}

Originally developed as an Italian sword-and-sandal project, the cooperation of the Greek government allowed the producers to complete the production on a budget of 500,000 GBP (equivalent to £11,348,087 in 2021) or approximately US$1,350,000 (equivalent to $13,598,020 in 2023), roughly twice the amount of contemporary Italian peplum films.

The 300 Spartans was the last film of Richard Egan's seven-year contract with 20th Century Fox. It was also the last film appearance of David Farrar, who retired from acting.^{[citation needed]}

In 1970, despite the film's Cold War connotations, it was dubbed in Russian and shown in the Soviet Union. The film proved to be very popular, with 27.1 million total viewers.^[5]

In a contemporary review for The New York Times, critic A. H. Weiler wrote: "In 'The 300 Spartans,' filmed in glorious color in authentic settings in Greece and other areas abroad ... this historic highlight has become a standard melodrama. In its seemingly dedicated efforts, Twentieth Century-Fox, the producer, has come up with an Eastern Western that is plagued by an excess of stilted, stylized dialogue and a minimum of genuine, colorful action that recently has been typical of cinematic forays into our storied past. ... A viewer now can see by what means the Persians and the Greeks annihilated each other, but beyond that it is shallow stuff no more memorable than a weather report, dated 480 B. C."^[6]

• Comic book: Dell Movie Classic: Lion of Sparta (January 1963)^[7][8]
• Novelization: The 300 Spartans by John Burke, first printed in 1962^[9]

Frank Miller's 1998 graphic novel 300 also depicts the Battle of Thermopylae. Miller viewed The 300 Spartans as a boy and said that "it changed the course of my creative life."^[10] In 2006, his book was adapted into a successful film of the same name directed by Zack Snyder.^[11]

• List of American films of 1962
• List of historical drama films
• 300, 2006 film
• 300: Rise of an Empire, 2014 film

• The 300 Spartans at IMDb  
• The 300 Spartans! at AllMovie
• The 300 Spartans at the TCM Movie Database
• The 300 Spartans at the American Film Institute Catalog
• The 300 Spartans (1962) at DBCult Film Institute
• The 300 Spartans publicity photos Archived January 31, 2016, at the Wayback Machine at 300spartanwarriors.com