Techniques and industry involved in the assembly and erection of structures. Early humans built primarily for shelter, using simple methods. Building materials came from the land, and fabrication was dictated by the limits of the materials and the builder's hands. The erection sequence involved, as now, first placing a foundation (or using the ground). The builder erected the structural system; the structural material (masonry, mud, or logs) served as both skeleton and enclosure. Traditional bearing-wall and post-and-beam systems eventually gave way to framed structures, and builders became adept at sealing and fireproofing with a variety of claddings (exterior coverings) and finishes. Steel-framed buildings are usually enclosed by curtain walls. In modern-day construction, sheathing the skeleton of the building is only the beginning; specialists then begin the bulk of the work inside, installing plumbing, electrical wiring, HVAC (heating, ventilating, and air-conditioning), windows, floor coverings, plasterwork, moldings, ceramic tile, cabinets, and other features. See also architecture