Stairs
a succession of steps raised one above the other, affording means of communication between two points at different heights in a building, etc.
Originally the stairs were placed from story to story in straight flights, like ladders, and were often external, being sheltered by a projection from the roof, but to save space the sp spiral form was adopted, the stair being contained in a cylindrical building projecting from the outside of the edifice. In this construction a central axis or newel reaching from the ground to the roof serves to support the inner ends of the steps, and the outer ends are let into the walls. The spiral form is still used in certain circumstances, but the finest stairs are now constructed in straight sections separated from each other by a wide step or platform called a landing.