SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
Scheme devised by Leonardo to repel the storming of ramparts by means of dislodging scaling ladders. In the drawing the outer beam of a horizontal framework slotted through the parapet walls pushes away four ladders. The framework is attached to a vertical beam pivoting at a point about two-thirds of the vertical height. A rope connected to the base of the beam passes through a pulley on the wall and is being hauled by two figures thus drawing the framework back. When the device is retracted, it is operated by pulling on a rope attached directly to the base. The further drawing shows a form of windlass or winch mechanism about to go into action. The text and adjacent sketch describes the pivoting mechanism. The leverage obtained provides the extra force necessary to dislodge attackers when they are more than halfway up the ladders.
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