Rigging systems and controls have been used in theaters since as early as the 15th century. Originally the rigging consisted of wood pulleys and sand bags. Sailors were typically hired to operate the rigging because of their experience with ropes and heights. Today's modern rigging consists of steel sheaves, wire cables and steel counterweights. Fly towers and catwalks are used to run the rigging, lights and curtains. Many of today's systems are motorized and computer operated. Design and installation of stage rigging and equipment should be done by a professional to insure proper function and safety.