A shoe is an item of footwear intended to protect and comfort the human foot while doing various activities. Shoes are also used as an item of decoration. The design of shoes has varied enormously through time and from culture to culture, with appearance originally being tied to function. Additionally, fashion has often dictated many design elements, such as whether shoes have very high heels or flat ones. Contemporary footwear varies widely in style, complexity and cost. Basic sandals may consist of only a thin sole and simple strap. High fashion shoes may be made of very expensive materials in complex construction and sell for thousands of dollars a pair. Other shoes are for very specific purposes, such as boots designed specifically for mountaineering or skiing. Traditionally, shoes have been made from leather, wood or canvas, but are increasingly made from rubber, plastics, and other petrochemical-derived materials. Though it has evolved over hundreds of thousands of years in relation to vastly varied terrain and climate conditions, the human foot is still vulnerable to environmental hazards such as sharp rocks and hot ground, against which, shoes can protect.