Cooperate to Build a Castle – Compete to Control It! In Castellan, two players work together to build a castle. Wall and tower pieces link together to form courtyards. When you finish a courtyard, you’ll claim it with a Keep. The more towers in your courtyard, the higher it scores. Your cards determine what pieces you get each turn . . . but you decide where to put them. If you’re clever, the pieces played by your opponent can end up scoring for you!