§ 33 Pictorial Mosaics for Walls, etc.
Therefore, this mosaic work appearing to them a picture, capable of resisting to all eternity water, wind, and sunshine, and because they considered such work much more effective far off than near, the ancients disposed it so as to decorate vaults and walls, where such things had to be seen at a distance, for at a distance one would not perceive the pieces of mosaic which when near are easily distinguished. Then because the mosaics were lustrous and withstood water and damp, it was thought that such work might be made of glass, and so it was done, and producing hereby the most beautiful effect they adorned their temples and other places with it, as we still see in our own days at Rome in the Temple of Bacchus145 and elsewhere.146 Just as from marble mosaics are derived those which we now call in our time glass mosaics, so from the mosaic of glass we have passed on to egg-shell mosaic,147 and from this to the mosaic in which figures and groups in light and shade are formed entirely of tesserae, though the effect is like painting; this we shall describe in its own place in the chapters on that art.[148]