Marion Harry Alexander Spielmann, 1911 Encyclopædia Britannica, Volume 23… (1911)
“ The Persians, the Etruscans and the Greeks carried on the art to the highest perfection, alike in sculpture and architectural ornament, and they applied it to gem sculpture, as in the case of “cameo.” Similarly, the inverse treatment of relief—that is, sunk below the surface, in order that when used for seals a true relief is obtained—was early brought to great completeness; this form of engraving is called “intaglio.” The degree of projection in relief, broadly speaking, has varied greatly with the periods of art. Thus, in Byzantine and Romanesque art the relief was low. ”
