Roman Floors and Ceilings
Houses of the poor in ancient Rome had floors (solum) of the first story which were made by smoothing the ground between the walls, covering it densely with small pieces of stone, bricks, tile, and potsherds, and pounding the whole lot down solidly and smoothly with a heavy rammer (fistuca). Such floors were called pavimentum, but the name eventually was used for floors of all types.
In houses of wealthy Romans the floor was made of stone slabs fitted smoothly together while very grand houses and mansions had concrete floors. Floors of upper stories were sometimes made of wood, but concrete was used here, too, poured over a temporary wood flooring. Such floors were very heavy, and required strong walls to support them ; examples are preserved of floors with a thickness of eighteen inches and a span of twenty feet.
A floor of this kind made an ideal ceiling for the room below, needing only a finish of stucco. Other Roman ceilings were made much as they are now: laths were nailed on the stringers or rafters and covered with mortar and stucco.