Stringer, Stringer Board: These are the structural supports that run along both sides of the stair case, frequently holding and supporting the treads and risers. The stringer is made of wood or steel. The top of the stringer is called the cap rail. A staircase is a set of stairs. A staircase can be internal, within a building, or it can be an exterior walkway. In construction, stairs are often referred to by their constituent parts: the steps for an interior staircase, the treads and risers for an exterior staircase. Staircases come in many shapes and sizes. They usually consist of multiple steps led upward from a lower level to a higher level, but they may also go in the other direction (from higher to lower). Stairs are used for walking up and down buildings, as well as for traveling from one floor to another. The word "staircase" is also used metaphorically to describe any rapid rise in status or power. People have been using stairs as a mode of transportation for as long as there have been stairs. The earliest evidence of this comes from Egypt, where workers used to climb up ladders to attach strings to the tops of pillars for taming wild animals. From here, they would slide down the strings into battle.