In Thebai, players take on the role of influential chieftains from noble families during the tumultuous period of the Late Bronze Age. Throughout the game, players must rebuild the Cadmea, the citadel of Thebes, while restoring the city's exports, praying to the gods of the city, and protecting the lives of the citizens as great heroes kill each other outside the gates.

The game takes place in 10 rounds, each divided into an action phase and a fate phase. During the action phase, players use a Citizen die and then move their Archon to the Cadmea. During the Fate Phase, players can earn additional points, depending on their accomplishments and protecting the city gates. After the final countdown, the player with the most victory points wins the game.