Pavements of the best building period can be recognised by the size of the cubes, about three to the inch, and by the neatness and finish of the work. Two varieties of mosaic can be distinguished, that in which marbles, stones, and coloured glass are cut into cubes only and the so-called _sectile_ mosaic in which elaborate scenes and groups of figures are represented, the coloured pieces being sawn into shapes to fit in with the design. The _Tablinum_ in the house of the vestals and the temple of Jupiter on the Capitol were paved with sectile mosaic. The most brilliant mosaic which came into use during the Empire for the decoration of walls and vaults was made of fragments of coloured marble and glass, the latter specially prepared with acids to make it opaque and to give it a brilliant appearance. The art of mosaic work has never died out entirely in Rome. The Roman mosaic pavements and mosaic wall decoration were copied by the builders of mediaeval churches, and even now a mosaic factory is kept up at the Vatican. Although first used in this way, coloured marbles were gradually employed for the interior decoration of houses, for columns, dados, and friezes. Lucius Crassus, the consul (176 B.C.), was the first so to adorn his house, and Lucullus (151 B.C.) paved his hall with black marble. Later, entire rooms were lined with thin slabs clamped to the concrete wall with iron. Sometimes such marble walls were given a thin coat of stucco and painted. As the passion for sumptuous interiors grew all the decorative arts were put into requisition. Walls were painted in fresco, as we can still see at Pompeii and in the house of Germanicus on the Palatine. Ceilings, walls, and cornices were ornamented in stucco in shallow relief. An extremely hard stucco was made with lime and powdered marble--it was nearly as durable as marble and could take almost as high a polish. It was even used for floors; for internal decoration, plaster of Paris was mixed with it. Mouldings, figures, arabesques, groups and scenes were worked in this stucco and delicately coloured. Examples have been preserved in the Diocletian museum and can be seen _in situ_ in the Latin tombs.