Athens Besieged is set within the Long Walls of Athens during the winter of 405-404 BCE. In the Fall of 405 Sparta destroyed the Athenian fleet at Aegospotami (near the straits leading to the Black Sea). The Spartan fleet then blockaded Piraeus harbor, and Spartan soldiers, augmented by their allies from Thebes and Corinth, camped outside the walls of Athens and lay siege to the city. By December, when the game begins, the city had exhausted its food supply.

The main location of the microgame is the Pnyx, where the Athenian Assembly must determine whether to surrender and relinquish its democracy. At the end of each month (10 minutes in class time), some Athenians die of starvation and disease; these players, on leaving the room, are assigned new roles as commanders of the Spartan and allied armies, as either of the two Spartan kings, as the Delphic Oracle, or in one or two other complicating roles. These “reincarnated” players now are thrust into a new debate: whether, after surrender, the Athenian men should be executed and the women and children enslaved, or whether the city should be preserved as a vassal state within a new Spartan empire. The Spartan kings, being advised by various generals in their war council, and by the Delphic Oracle, determine the outcome of the game—and the fate of Athens.