Centurion: Defender of Rome is set in ancient times, where you start as a young Roman legionnaire. Your goal is to conquer the known world through force or diplomacy, fighting on land and sea. You begin with one province, Rome, and one legion. To complete the game, you must conquer all provinces on the map.
The gameplay involves both turn-based strategy and action mini-games. As a ruler, you manage your provinces by setting tax rates and making people happy by organizing games in Rome. This can include chariot races, gladiatorial combat, or simulated naval battles. These actions start mini-games where you control the participants.
Another part of the game is military conquest. You can raise legions or strengthen them in any province you control. There are three types of legions, each with different strengths. You can also move a legion to a neighboring province. When you enter an uncontrolled province, you can speak with its ruler and try to convince them to give it to you for free.
When your legion attacks or defends a province, the game switches to an isometric view of the battlefield. You can give orders to your legion and watch as they fight against enemy forces. The outcome depends on the strength of both sides.
Finally, you can buy warships and engage in naval battles with enemy fleets. These are represented as action mini-games, but the outcome depends on the strength of your fleet.