Age of Mythology: The Titans is an expansion pack to the real-time strategy video game of Age of Mythology. It was developed by Ensemble Studios and released on September 30, 2003. It was followed in 2016 by a second expansion pack to the original game called Tale of the Dragon. The Titans adds a fourth culture to the game, the Atlanteans, and three new major gods, plus new units, buildings and god powers. It also includes many new features, such as auto-queueing (allows indefinite training of units as long as you have sufficient resources), and the ability to summon a Titan, a gargantuan, godlike being that forms the game's focal point.

The story begins with Kronos, who is still trapped in Tartarus, watching the Atlanteans, who are attempting to survive the harsh winters in the Norselands after Atlantis was destroyed 10 years ago in the events of Age of Mythology. He sends his unnamed servant to the colony, who kills the Theocrat Krios and possesses his body. Krios tells of a temple he saw in a vision. The Atlanteans leave the Norselands by using the foreseen temple called a Sky Passage, and they come to a resourceful island. Upon their arrival, Krios points out the plant-covered Temples to Oranos and Kronos. He convinces everyone including Kastor to worship them. This angers the Greeks, who promptly attack them. The Atlanteans retaliate by destroying the entire Greek colony. The survivors tell of their defeat to General Melagius. The Atlanteans invade Melagius' city called Sikyos, and slay him. Just as the Atlanteans kill Melagius, his Egyptian and Norse allies come to aid the city. Kastor decides they are too powerful and retreats. He decides to attack their homelands while they are heavily defending Greece. In the Norselands, Kastor destroys Norse temples and replaces them with Atlantean temples, to show his superiority. He also destroys the Tower of Odin (Odin's only stronghold on Earth) by using a god power from Kronos. Some Atlantean forces then sail to Egypt. Queen Amanra is warned by Arkantos that the Atlanteans are coming to steal relics from the Egyptians. Amanra fortifies the protections around the relics, but the Atlanteans still manage to steal them. Arkantos protects Amanra from Atlantean soldiers then tells her that Kastor is being tricked. He tells her to find Kastor and to help him. Meanwhile, Krios congratulates Kastor on his work and shows him a Sky Passage that he has found, which will take him behind Greek lines. Kastor enters it and finds himself on Mount Olympus. Using special temples that change his men into different myth units, Kastor slays the followers of the Olympian Gods, including Odysseus. However, once he does this, the temple to Zeus on the mountain collapses. Back in Greek territories, the Titan Prometheus and his army of Prometheans from Tartarus are destroying Sikyos. Krios arrives and announces that Kastor's actions in Greece, Egypt and the Norselands, combined with his invasion of Olympus, have weakened the Olympian Gods' control over these territories and allowed minor titans to spawn. Krios reveals his true form, a winged demon and servant of Kronos, and flees.