A shoe is an item of footwear intended to protect and comfort the human foot. Shoes are also used as an item of decoration and fashion. The design of shoes has varied enormously through time and from culture to culture, with appearance originally being tied to function. Though the human foot is adapted to varied terrain and climate conditions, it is still vulnerable to environmental hazards such as sharp rocks and temperature extremes, which shoes protect against. Some shoes are worn as safety equipment, such as steel-soled boots which are required on construction sites. Additionally, fashion has often dictated many design elements, such as whether shoes have very high heels or flat ones. High fashion shoes made by famous designers may be made of expensive materials, use complex construction and sell for hundreds or even thousands of dollars a pair.