FLOOR, the lower horizontal surface of a room; used, also, almost interchangeably with storey (q.v.), to designate the dif ferent levels or planes of rooms, one above the other, as ground floor, first floor, etc. Floors were, at first, simply of tamped earth (beaten down), covered with textiles or skins; later, all types of stone pavings were introduced; in Roman times floors of cement or terrazzo (small pieces of marble imbedded in cement) were common, as well as mosaic and marble floors, often of great rich ness. During the middle ages the use of tiles for floors increased; they seem to have been the rule in the great churches. Wooden floors appear early, especially in domestic work and in buildings of many storeys (where their support by wooden beams is a simple matter). At the present time wooden floors are usually double (see BUILDING; CARPENTRY; MOSAIC).