The story takes place in the fertile, eastern lands bordered by the Mediterranean Sea and kept by the gods. Within the cradle of ancient civilization empires are built, wars fought, alliances forged, and heroes born.
Agamemnon (Brian Cox
), king of Mycenae, has united most of Greece's kingdoms under his rule and now advances his army upon the nation of Thessaly, hoping to include it in his collection of ever-growing conquests. King Triopas (Julian Glover
) bargains with Agamemnon to each let one of their best fighters decide who wins the battle rather than engaging in open war. Triopas calls upon the giant Boagrius (Nathan Jones
) while Agamemnon calls to Achilles, but the legendary warrior is nowhere to be found. A messenger boy (Jacob Smith
) is sent to fetch him and Agamemnon curses the stubborn nature of the fiercest warrior Greece has ever seen. A half-god and blessed with incomparable strength and skill, Achilles lives to fight but he refuses to associate with Agamemnon, preferring instead to seek his own destiny and be immortalized in history. Achilles easily defeats Boagrius, sealing Agamemnon's control over the nation, and calls out if there is anyone else worthy enough to fight him.
Meanwhile, Prince Hector (Eric Bana
) and Paris (Orlando Bloom
) of Troy feast in the banquet hall of King Menelaus of Sparta (Brendan Gleeson
) as honored guests and peace ambassadors to their home nation. However, young Paris sneaks away to be with Menelaus' beautiful wife, Helen (Diane Kruger
), whom he loves dearly. He convinces her to come back with him to Troy, stowing her away on his brother's ship. When Hector finds out he is clearly angry but it is too late to return to Sparta with Helen and seek pardon. Finding Helen gone, Menelaus vows revenge on Troy and seeks the approval of his brother, Agamemnon, who is only too happy to oblige, though Agamemnon's decision comes mostly from his desire to sack Troy.
Odysseus (Sean Bean
), king of Ithaca and under command of Agamemnon, goes to convince Achilles to accompany them in the conquest of Troy. He finds him sparring with his young cousin, Patroclus (Garrett Hedlund
), who is more than eager to join in the fighting. But Achilles refuses to go, despite Odysseus' assurance that this war will go down into history. Achilles later seeks advice from his mother, the sea nymph Thetis (Julie Christie
), who is gathering shells to make a new necklace for him. She tells him that if he chooses to stay home he will find a wife, raise a family, and die old and loved. If he goes to Troy, he will find his eternal glory and history will remember his name for thousands of years. However, should he go to Troy, he is doomed to die and will never return.
Meanwhile, Hector and Paris return to Troy with Helen, greeted warmly by their fellow Trojans. The city is guarded by a high, thick wall that has remained impenetrable since its founding. They meet their father, King Priam (Peter O'Toole
), who welcomes Helen and praises her beauty. Hector is reunited with his wife, Andromache (Saffron Burrows
), and his infant son.
Achilles decides to join Agamemnon's campaign against Troy but brings his own warriors, the Myrmidons, led by Eudorus (Vincent Regan
). Patroclus accompanies them as well. The Myrmidons prove to be faster rowers than the Greeks and arrive on the shores of Troy before anyone else, though Achilles tells Patroclus to stay and watch the ship. They take the beach with ease and sack the Temple of Apollo where priestess and cousin of Hector and Paris, Briseis (Rose Byrne
), is taken captive. In a defiant move, Achilles decapitates the statue of Apollo. Prince Hector leads an offensive to keep the Greeks at bay and runs into the temple where Achilles confronts him but refuses to fight him. Achilles explains that their fight would be suited best in front of an audience and he allows Hector to leave.
Briseis is brought to Achilles' hut as his prize. She berates him for killing priests of Apollo before he is summoned to see Agamemnon who is preparing to celebrate the victory. There, tensions rise as Achilles and the king argue over claims to the victory. Agamemnon goes further by bringing in Briseis, claiming her as his own spoil of war, which drives Achilles into a rage. He threatens to fight for her but she angrily interjects, saying that no one else will die for her. Achilles stays his blade, to the surprise of Agamemnon. Achilles vows that Agamemnon will one day fall under his sword.
That night, Priam seeks the advice of his advisors and elders with his sons in attendance, discussing how best to defend against the Greeks. Paris offers an alternative to bloodshed; he will fight Menelaus for Helen's hand. The winner will take her home and the loser will burn before nightfall. Later, Priam speaks with Paris in a courtyard and admits that, in all the wars hes fought for power or land, a war fought for love makes more sense. He gives Paris the Sword of Troy, forged at its founding and containing the history of their nation. He explains that as long as a Trojan wields it there is hope for their people.
Hector goes to see his wife and son. She fears for his life and can't imagine living on without him. He comforts her before getting up to see his brother. In the halls, he sees a cloaked figure and gives pursuit to find that it's Helen trying to leave the city. She is remorseful for being the sole reason so many Trojan men died that day but Hector tells her that returning to Menelaus will not end the war and that she is a princess of Troy now. Helen returns to Paris.
The next day, Agamemnon's army marches for Troy while Achilles, still seething over his loss of Briseis, watches from a nearby hill with his men. Hector and Paris ride out to meet Agamemnon and Menelaus before battle. Agamemnon demands that the Trojans return Helen to his brother and submit to his rule. Hector bravely rebuffs but Paris offers to fight Menelaus one-on-one, hoping that will settle the dispute. While Agamemnon could care less about returning Helen to his brother, he allows Menelaus the opportunity to issue revenge. The two begin their fight and Menelaus is clearly stronger. Paris is wounded and disarmed but, before Menelaus can deliver a death blow, ducks away and crawls back to his brother. Stunned at his cowardice, Menelaus demands the fight to continue but Hector defends his brother and drives his sword through Menelaus, killing him. Enraged, Agamemnon charges forward with his army.
Watching from his hilltop, Achilles can't help but curse under his breath at Agamemnon's inability to keep his ranks in formation. Hector proves to be the more able warrior and overpowers the Greeks with his tactics. One of the strongest Greek warriors, Ajax (Tyler Mane
) is felled by Hector. Odysseus advises Agamemnon to fall back before he loses his entire army and the Greeks retreat to the beach where their archers provide defense.
With Menelaus dead, the main reason for the assault on Troy is gone and Agamemnon struggles to think of a way to rally the troops to his cause. Odysseus suggests that Agamemnon put his reservations aside and enlist Achilles to fight again. Outside, Briseis is tossed around between Greek soldiers, having been given to them by Agamemnon. Before she can be cruelly branded, Achilles steps in and takes her back to his hut. He gives her a wet cloth to clean with and some food. When she questions why he fights and defies the gods, he shows her a more reflective side to his nature and explains that the gods are jealous of men for their short, mortal lives. As such, everything is more beautiful.
Priam consults with his advisors again while Paris laments over his cowardice. Helen assures him that, though Menelaus was a strong warrior, she hated her life with him. She'd rather have someone to love and grow old with than to see him die on the battlefield. Hector advises his father that the Greeks underestimated Trojan strength and that they should not do the same. However, General Glaucus (James Cosmo
) wants to strike preemptively and High Priest Archeptolemus (Nigel Terry
) claims Troy is favored by the gods, citing bird omens. Despite Hector's warnings to keep behind their walls, Priam favors his advisors and issues an attack before daybreak.
As Achilles sleeps that night, Briseis takes a dagger and holds it to his throat. Without opening his eyes, he encourages her to kill him but she hesitates. They realize their feelings for each other and make love. Achilles decides that he's had enough of war and offers to take Briseis away from Troy. Afterwards, he speaks with Eudorus and tells him that they will go home. Hearing this, Patroclus is devastated, having hoped to take part in battle. Achilles returns to his hut.
Just as dawn approaches, the Trojan army, led by Hector, set up on the dunes and sent hundreds of lit arrows into the sand. The Greeks awake in time to see large balls of hay being rolled down the hill towards camp, ignited in huge fireballs by the torched arrows. Banging their shields to intimidate, the Trojans advance towards the Greek camp. Suddenly, Achilles appears in his armor and rallies the troops to fight. Achilles fights his way towards Hector and the two engage in combat. Greeks and Trojans alike surround them, edging them on, until Hector slits Achilles' throat with a swift thrust of the sword. Achilles falls, gasping for breath, while the Myrmidons look on in horror. But when Hector removes his helmet, he discovers that the man he wounded is not Achilles; its Patroclus. Hector, repentant but resolute, drives his sword into the boy's chest to finish him. He addresses Odysseus and tells him they've fought enough that day. Before leaving, Odysseus tells Hector that Patroclus was Achilles' cousin.
The Myrmidons return to camp as Achilles emerges from his tent. Seeing them battle-worn, he asks why they disobeyed him. Eudorus laments that Patroclus disguised himself in Achilles' armor, even moved like him, and fell under Hector. Achilles is outraged and attacks Eudorus. Briseis tries to stop him but he throws her to the ground.
Hector returns to his wife. He admits that he killed a boy who was much too young and feels that his actions will have severe repercussions. He shows his wife a hidden passage under Troy that she can take civilians through to get to the mountains should he die and the walls be breached. Though she is upset to have to consider this, she heeds his advice.
Achilles puts his cousin on a funeral pyre and sets it alight. Agamemnon watches and says, "That boy may have just saved the war for us," knowing that the rage of Achilles will not wane until he's had revenge. Meanwhile, Helen watches as Paris practices his archery in preparation for battle, hitting his target time and again.
The following morning, Achilles sets off to enact vengeance upon Hector. Briseis begs him not to go, but he ignores her. He rides to the gates of Troy and calls for Hector who dresses in his armor and says goodbye to his wife. He meets Achilles outside alone. Achilles throws down his helmet so that Hector can see his face. Though Hector tries to reason, Achilles is bent on bloodlust. As they begin to fight, Priam and Paris watch while Helen comforts Andromache who can't bring herself to look. Achilles overpowers Hector by driving his spear into his chest before finishing him with his sword. He then ties Hector's legs together behind his chariot and drags him away, back to the beach. When he returns to his hut, Briseis cries out and asks when the killing will stop before leaving.
That night, Achilles is visited by a stranger in a cloak. The stranger kisses Achilles' hand before revealing himself as none other than King Priam. Having stealthily entered the Greek camp unnoticed, Priam begs for his son's body back to be given a proper burial. He tells Achilles that, while Hector killed his cousin, he did not know who it was and he asks Achilles how many cousins and brothers he's killed in his time. Despite being enemies, he asks for respect. Achilles relents. He weeps over Hector's body, promising to meet him in the next life, before giving him to Priam. When Briseis comes forward, Achilles allows her to go home and apologizes for hurting her. He gives Priam his word that the Greeks will not attack Troy for 12 days to allot for proper mourning.
When Agamemnon hears of Achilles' secret treaty with Priam, he becomes incensed. But Odysseus, who notices the sculpture of a horse a fellow soldier has made for his son, proposes a plan, putting the 12 days of mourning to their advantage.
After 12 days, the Trojans discover that the beach has been abandoned and various bodies lie in the sand. They appear to have been taken by disease and, where the heart of the camp once was, a large wooden horse has been erected. Upon seeing this, Priam is advised that the horse was left as a gift to the god Poseidon and is encouraged to bring it back to Troy. Paris, who is suspicious, urges his father to burn the horse, but Priam brings the horse into the city where its revered as a sign of the end of the war. A Trojan scout, hiking through the cliffs outside the city, comes upon a cove apart from the main beach and discovers the Greek armada hiding there. However, he is killed by arrow before he can warn the rest of Troy.
Meanwhile, the whole city celebrates into the night. Once everything has quieted down, the horse opens and Achilles, Odysseus, and a mass of Greek soldiers emerge from inside and open Troy's gates where the rest of the Greek army has gathered. They quickly infiltrate the city, pillaging and burning homes and killing any Trojan who stands in their way while a tearful Priam can only watch. Soldiers of Troy attempt to defend the royal palace, but fail. As Priam prays before the statue of Apollo and asks why he's been forsaken, Agamemnon comes up behind him and stabs him in the back. Achilles, meanwhile, searches the city for Briseis.
Paris and Andromache lead surviving civilians down to the secret passage where Paris gives a young boy, Aeneas (Frankie Fitzgerald
) (a progenitor of the Romans), the Sword of Troy, reciting what his father told him. He then returns with his bow and arrow to help fight.
Briseis is praying before a statue of Apollo when she is grabbed from behind by Agamemnon. Achilles sees this and runs to her aid. Agamemnon tells Briseis his intent to take her back to Greece as his slave before she takes a concealed knife and fatally stabs him in the neck. His guards accost her but Achilles kills them. As he is helping her up, Paris arrives and shoots an arrow through Achilles' heel. Standing up to face Paris, despite Briseis' cries, Achilles is shot again through the chest. He removes the arrow only to be shot again and again, each time removing the arrow. He finally collapses and tells Briseis that she was his peace in a lifetime of war and urges her to escape. Briseis goes with Paris and they leave as the Greeks arrive at the palace to find Achilles dead, seemingly taken by a single shot to the heel (thus perpetuating the myth surrounding his death).
Achilles' body is burned honorably on a funeral pyre within the ruins of Troy the following day as Odysseus watches and exalts, "If they ever tell my story, let them say I walked with giants. Men rise and fall like the winter wheat, but these names will never die. Let them say I lived in the time of Hector, tamer of horses. Let them say I lived in the time of Achilles."