Crenelation Screens Castle defenders would often install temporary wooden screens to further protect the castle wall defenders. The screens would pivot up to allow the defenders to drop rocks on attackers or fire ranged weapons. The crenelation screens shown below consists of a U frame measured to fit inside the crenel and a screen made of thin strips of balsa. The screen element was not glued to allow it to move. In fact, the prototype was not even hinged at all and relied on a tight fit inside the crenel.    Screen (open and closed) New versions are planned with a pivot built into U frame.