[6] For origin of mosaic work see Pliny xxv., xxxiii., xxxv. See also the Iconographic Encyclopædia, by Heck, translated from the German by Spencer F. Baird, New York, 1851, vol. ii. p. 77, &c., and Fosbroke's Cyclopædia of Antiquities, 1840.
[7] See Art of Illumination, 1844, and Illuminated Books of the Middle Ages, 1849. By Henry Noel Humphreys.
[8] For more on this subject see the Nouveau Traité de Diplomatie of the Benedictines.
[9] Brown's Sacred Architecture, 1845, pp. 24, 25.
[10] Brown's Sacred Architecture, 1845.
[11] Cadell's Italy, vol. ii. p. 339.
[12] For a very interesting description of this feature in Byzantine work see The Stones of Venice, by John Ruskin, vol. ii.
[13] Ruskin's Crown of Wild Olive, Introduction.
[14] For an account of Christian Symbolism, see Mrs. Jameson's Sacred and Legendary Art.
[15] See A New History of Painting in Italy. By J. A. Crowe and G. B. Cavalcaselle, 1864; vol. i. chap. 4.