Note 6 — Chapter II · ART IN ITALY IN THE THIRTEENTH CENTURY.
Reading edition
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.