The function of battlements in war is to protect the defenders by giving them part of the parapet to hide behind, from which they can quickly expose themselves to launch projectiles, then retreat behind the parapet. A defensive building might be designed and built with battlements, or a manor house might be fortified by adding battlements, where no parapet previously existed, or cutting crenellations into its existing parapet wall. A distinctive feature of late medieval English church architecture is to crenellate the tops of church towers, and often the tops of lower walls. These are essentially decorative rather than functional, as are many examples on secular buildings.