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A murder hole or meurtrière is a hole in the ceiling of a gateway or passageway in a fortification through which the defenders could fire, throw or pour harmful substances or objects, such as rocks, arrows, scalding water, hot sand, quicklime, tar, or boiling oil, down on attackers. They also allowed water to be poured onto fires started within the gate passage. Similar holes, called machicolations, were often located in the curtain walls of castles, fortified manor houses, and city walls. The parapet would project over corbels so that holes would be located over the exterior face of the wall, allowing the defenders to target attackers at the base of the wall.