Sparta is the Greek city-state from which Kassandra or Alexios originally comes in Assassin's Creed Odyssey.
The player chooses either Kassandra or Alexios as the protagonist, but both represent the same family line and begin the story as a Spartan descendant. Their childhood is tied to Sparta, Mount Taygetos, and the rigid warrior culture associated with the city-state. The opening events eventually lead the protagonist away from Greece's Peloponnese and into a wider journey across the Aegean world.
Odyssey uses historical settings and figures from the fifth century BCE while allowing players to change parts of the protagonist's personal story. Athens is another major city in the game and a major center of the historical Peloponnesian War, making it a common but incorrect answer to this question.