Minecraft wiki entry for Defense, associated text: If you have a bow or crossbow and arrows, this is a good way to kill mobs (and perhaps players) that get within range is murder holes. Often incorrectly described as "holes in the ground", the actual term is a hole in a ceiling or gateway, in which defenders can fire at enemies. To make one, extend an overhang over your walls to 5-6 blocks outward. Be sure to add battlements. After you've done that, dig a 1-block hole in the floor every little bit, so no bit of ground is uncovered. You can optionally add trapdoors. Make sure to build it off the ground so that creepers cannot blow up while you are looking through a murder hole. This also adds to the overall safety, as you do not have to lean over the walls and subject yourself to skeleton arrow fire when you're sniping a zombie.