The main story of Assassin's Creed Odyssey begins in 431 BCE.
This date places the game at the beginning of the Peloponnesian War between Athens and Sparta. The player controls either Kassandra or Alexios, a choice that changes the selected protagonist but not the historical starting year of the main story.
Odyssey is set across the Greek world, including mainland Greece and numerous Aegean islands. Its narrative combines the fictional life of the player character with real historical figures and events associated with the conflict between Athens and Sparta. The game also includes a much earlier Spartan prologue at Thermopylae, which can make the chronology seem more complicated.
The year 404 BCE marks the end of the Peloponnesian War, not its beginning. Assassin's Creed Odyssey was released in 2018 and is designed as a role-playing game with dialogue choices, branching quests, and multiple possible endings.