The creation of the Philadelphia city skyline required many engineering disciplines. Civil engineers designed the steel or concrete structure that allows the building to stand and provides the clean water and waste water systems. Mechanical engineers create the heating, ventilation, and air conditioning systems that allow people to live, work, and play comfortably in the building. Electrical engineers provide the electrical systems that power the mechanical systems, provide lighting, and powers the many electrical devices used. Materials engineers develop the best materials for use in all aspects of the building.