Assassin's Creed Odyssey is primarily set in 431 BCE.
The game opens during the early part of the Peloponnesian War, the long conflict between Athens and Sparta. Its historical campaign follows a Spartan mercenary, either Kassandra or Alexios, across the Greek world. Players visit mainland Greece, the Aegean islands, and other territories while becoming involved in family, political, and mythical storylines.
The date 431 BCE marks the beginning of the Peloponnesian War, which is also the principal historical framework of the game. Odyssey uses real figures such as Pericles, Socrates, and Hippocrates, but it combines documented history with fictional characters and speculative mythology.
A common mix-up is placing Odyssey in the time of Alexander the Great, who lived later, or during the Roman period shown in other entries. Odyssey predates Assassin's Creed Origins, whose major events occur in the first century BCE. The game's modern-day sections take place much later than its Greek historical narrative.