Building materials included bones such as mammoth ribs, hide, stone, metal, bark, bamboo, clay, lime plaster, and more. For example, the first bridges made by humans were probably just wooden logs placed across a stream and later timber trackways. In addition to living in caves and rock shelters, the first buildings were simple shelters, tents like the Inuit's tupiq, and huts sometimes built as pit-houses meant to suit the basic needs of protection from the elements and sometimes as fortifications for safety such as the crannog. Built self-sufficiently by their inhabitants rather than by specialist builders, using locally available materials and traditional designs and methods which together are called vernacular architecture.