From the website:
In Assassin's Creed: Arena, players compete to uncover the best targets for assassination. But before you can go in for the kill, sometimes you have to deal with some pesky guards, as well as your opponents. Players will collect cards and treasure, move guards, and hide within the city of Constantinople until they find their time to strike. Combat is handled through cardplay, and the player who best manages their cards will have the best chance at victory.