+COLOR DECORATION.+ Plaster was also used as a ground for painting, executed in distemper or by the encaustic process, wax liquefied by a hot iron being the medium for applying the color in the latter case. Pompeii and Herculaneum furnish countless examples of brilliant wall-painting in which strong primary colors form the ground, and a semi-naturalistic, semi-fantastic representation of figures, architecture and landscape is mingled with festoons, vines, and purely conventional ornament. Mosaic was also employed to decorate floors and wall-spaces, and sometimes for ceilings.[13] The later imperial baths and palaces were especially rich in mosaic of the kind called opus Grecanicum, executed with numberless minute cubes of stone or glass, as in the Baths of Caracalla and the Villa of Hadrian at Tivoli. [Footnote 13: See Van Dyke’s _History of Paintings_, p. 33.] To the walls of monumental interiors, such as temples, basilicas, and thermæ, splendor of color was given by veneering them with thin slabs of rare and richly colored marble. No limit seems to have been placed upon the costliness or amount of these precious materials. Byzantine architecture borrowed from this practice its system of interior color decoration. CHAPTER IX. ROMAN ARCHITECTURE--_Continued_. BOOKS RECOMMENDED: Same as for Chapter VIII. Also, Guhl and Kohner, _Life of the Ancient Greeks and Romans_. Adams, _Ruins of the Palace of Spalato_. Burn, _Rome and the Campagna_. Cameron, _Roman Baths_. Mau, tr. by Kelcey, _Pompeii, its Life and Art_. Mazois, _Ruines de Pompeii_. Von Presuhn, _Die neueste Ausgrabungen zu Pompeii_. Wood, _Ruins of Palmyra and Baalbec_. +THE ETRUSCAN STYLE.+ Although the first Greek architects were employed in Rome as early as 493 B.C., the architecture of the Republic was practically Etruscan until nearly 100 B.C. Its monuments, consisting mainly of city walls, tombs, and temples, are all marked by a general uncouthness of detail, denoting a lack of artistic refinement, but they display considerable constructive skill. In the Etruscan walls we meet with both polygonal and regularly coursed masonry; in both kinds the true arch appears as the almost universal form for gates and openings. A famous example is the Augustan Gate at Perugia, a late work rebuilt about 40 B.C., but thoroughly Etruscan in style. At Volaterræ (Volterra) is another arched gate, and in Perugia fragments of still another appear built into the modern walls.