A freestanding, adjustable, modular spiral staircase embodied in a unique method of spiral staircase design is provided. The steps of the spiral staircase are arrayed and supported in a circular pattern around a central column with the outside edges or leading or trailing corners of the steps are supported by three peripheral columns, while step posts interconnect adjacent steps. Many parts are interchangeable and the steps adjustable to allow for shortening or lengthening the staircase. The base of the staircase unit is heavy to provide maximum stability and to prevent tipping.