Fall of the Trident is the main campaign in Age of Mythology. It follows the adventures of Arkantos and his allies.
The story starts off with the Atlantean hero, Arkantos, discussing with the Theocrat how they are losing Poseidon's favor. Pirates then start attacking Atlantis, whom Arkantos successfully drives off. However, as the pirates were fleeing, their leader, Kamos the minotaur, stole the trident from a Poseidon statue. Arkantos follows Kamos, gets the trident back, and unsuccessfully tries to kill Kamos, who flees on a Leviathan. He then proceeds to Greece where he fights in the Trojan War alongside the Greek heroes Ajax, Odysseus, and Agamemnon. Arkantos first destroys the ports of Troy, allowing Agamemnon's army to land. He then destroys the Trojan Gate and waits for Ajax's army to arrive and finish off the city. He learns from a messenger that Ajax is surrounded by Trojans; Arkantos goes to help him. After Arkantos rescues Ajax he destroys Troy's forward military base. Finding that Troy's gates are repaired again, Arkantos and Odysseus thinks of the Trojan Horse to help win the war. He has his villagers construct it (making sure no Trojan scouts find out about it) and then he, Ajax, and Arkantos enter it to sneak into Troy. They destroy the Trojan Gate from the inside, which allows Agamemnon’s army to enter. Together they obliterate the city.
After winning the war, Arkantos and Ajax sail to Ioklos to mend their ships, but end up rescuing the centaur Chiron from bandits who had taken over the city. Chiron tells them that the bandits had invaded Ioklos and taken all the men with them to their stronghold, which the three heroes raid. There they discover the Cyclops Gargarensis, who is the story's main antagonist, using the men to dig a passage into the Underworld. Gargarensis enters into the passage (using meteors to kill most of Arkantos's men), and the heroes follow him. They later prevent him from opening a strange gate in Tartarus.
In anger, Gargarensis traps the heroes in Tartarus. However, the heroes soon escape the underworld with the help of shades (robed living dead inhabitants of the Underworld) and Zeus, only to surface in Egypt. There, they help the Nubian warrior-woman Amanra dig up an ancient sword that is said to bring a statue, that serves the person who brings the sword to it, to life. The heroes bring the sword to the statue, which becomes animated. The statue, named the Guardian, destroys the rampaging army of Kemsyt, a common enemy and ally of Gargarensis who was in charge of the Ioklos bandits.
The protagonists then begin to assemble the pieces of the body of the Egyptian god Osiris, in order to bring him back to life and prevent Gargarensis from opening a similar underworld gate in Egypt. Amanra captures a piece of Osiris from Kemsyt, who flees on a Roc. Chiron gets the head of Osiris from a huge tamarisk tree with the help of a group of Norsemen who have tracked Gargarensis from the damage he did in their homeland. Arkantos and Ajax get a piece of Osiris from Kamos, whom Arkantos kills. Athena visits Arkantos in a dream to inform him that behind the gates is the imprisoned Titan Kronos, who has promised Gargarensis immortality in exchange for setting him free to conquer the world. According to her, the adamantine doors that seal Kronos in Tartarus can only be opened by a mortal. For this reason, Kronos uses Gargarensis to try to destroy the doors. In his dream, Arkantos destroys a "strangely familiar city," which turns out to be Atlantis. After this, Arkantos wakes up. The heroes bring all the pieces of Osiris in front of a pyramid dedicated to Osiris. Osiris is reborn and he crushes Gargarensis' forces before they open the Gate, forcing Gargarensis to the Norselands to open another gate there.
While the heroes are traveling to the Norselands in pursuit of Gargarensis, they see Odysseus' ship, which is now a wreck on the shore of an island. The protagonists land on the shore and see strangely-acting pigs. While the heroes look on, the sorceress Circe turns Arkantos and Ajax into boars. Arkantos and Ajax, now boars, bring the pigs and themselves to a temple of Zeus, where they get changed back into humans. Odysseus, who was alive, thanks them and the heroes continue their journey to the Norselands, arrive, and get caught in an avalanche, which was a trap Gargarensis set for them. They fight their way out of the pass they are caught in and help two dwarves, Eitri and Brokk, reclaim their forge that was captured by giants. The heroes then journey to Midgard, where they meet Skult, an elderly hermit, who says his flag can unite the warring Norse tribes. He offers to help them if they can get him safely through the giant lands. They accept the offer, and at one point, their path is blocked by a boulder wall. The heroes manage to break through just before giants close in on them. The heroes escape and hardly any distance later, their path is blocked again, this time by an impassable forest. They are only saved when Odin sets the forest on fire, causing the trees to fall and allowing them to flee. To the heroes' confusion the tribes start attacking them when they see Skult's flag. They discover Skult, who disappears, was a servant of Loki and Gargarensis. With the help of the valkyrie Reginleif they unite the Norse tribes by undertaking a series of quests for them. For the first chieftain, they rescue some dwarves that were captured by trolls. For the second chieftain, they help defend his town from giants. For the last chieftain, they rescue his daughter, Greta Forkbeard, from giants. They fight their way to the Well of Urd (under Gargarensis' control), which is a passage to the Underworld. They find he is trying to open the Underworld Gate again. However, they are beaten away from the Gate by powerful fire giants, and are only saved because Chiron gave his life causing a rock fall between the giants and themselves. The disheartened heroes however manage to save the day by helping Eitri and Brokk, who they meet again, reforge Thor's hammer Mjolnir, which is used to shut the Gate just in time. The area around the gate explodes, and the heroes get blasted out of the underworld.
After the heroes awake from their unconsciousness, they learn Gargarensis is furious and is sending an army to get them. The heroes withstand his rage and capture Gargarensis in a last mighty battle with the help of the Norse heroes and Odysseus, who arrives with an army, and decapitate him. Arkantos, Ajax, Amanra, and Odysseus then sail back to Atlantis, only to discover that it is under Gargarensis' control. Apparently the heroes were tricked into believing they had killed him when in fact they had killed Kemsyt, who used his magic to make himself look like Gargarensis. They then discover that the last gate to Tartarus is right under the great temple of Atlantis, and Gargarensis was attempting to open it.
Arkantos fights his way to the gate, evacuates the people, and, with the help of Zeus, who grants him demigod-like powers, defeats the powerful living statue of Poseidon that was guarding it. Gargarensis is killed as the crumbling statue's trident falls on him. Atlantis is torn to shreds by earthquakes, storms and meteor showers due to Poseidon's anger. The final scene of the story shows Athena making Arkantos a god for his momentous deeds.