With this expansion, the players have new possibilities of strengthening their influence in the area around Carcassonne. Now traveling merchants transport their goods to surrounding cities and monasteries. The cities in the surrounding countryside can increase to a size large enough to elect their own mayors. Simple farmers build large and wealthy farms and the church tries to strengthen their influence by establishing abbeys.
Mayors are pieces that rule over cities - and they're worth the number of pennants in that city. Abbeys are like Monasteries/Cloisters except you don't have to match their sites - they can fit in anywhere and finish whatever they connect to. Use barns to score on fields during the game (not just at the end) or wagons to move from a completed element to an unfinished one automatically.
This is a comprehensive expansion for Carcassonne that adds a lot of neat game play and new elements. It's definitely one that any fan should have in their collection.