Monastic culture has generally been seen as set apart from the medieval battlefield, as `those who prayed' were set apart from `those who fought'. However, in this first study of the place of war within medieval monastic culture, the author shows the limitations of this division. Through a wide reading of Latin sermons, letters, and hagiography, she identifies a monastic language of war that presented the monk as the archetypal `soldier of Christ' and his life of prayer as a continuous combat with the devil: indeed, monks' claims to supremacy on the spiritual battlefield grew even louder as Church leaders extended the title of `soldier of Christ' to lay knights and crusaders. So, while medieval monasteries have traditionally been portrayed as peaceful sanctuaries in a violent world, here the author demonstrates that monastic identity was negotiated through real and imaginary encounters with war, and that the concept of spiritual warfare informed virtually every aspect of life in the cloister.