190	NATURAL HISTORY OF GEMS.
	Emerald vase in general design ; but the size was perfectly incredible, the diameter over the handles measuring a Viennese ell all but two digits (about 27 inches). This also, to remove all doubt, is given of the full size upon the same gigantic folding plate. But what then gave it supreme importance, and probably had conduced chiefly to its pre­servation through the wreck of ages, was the inscription, " not made by hands," but traced by the finger of Nature (as the imperial librarian states, and evidently in good faith),* in the colours of the stone, B. XEISTO. ES. XXX., interpreted as " Christus Beator Orbis." To produce the effect of natural shades in the substance these letters must have been written with nitric acid, which leaves a slight but indelible opacity where applied, of which there is an example (Marlborough) known to myself, the name and titles of a former owner, Andreas Carraia, traced round the edge of a singularly fine Cameo (Constantine with helmed head). The mixture of Greek and Roman capitals betrays a Byzantine date, and seemingly refers to the con­secration of this unparalleled relic of imperial splendour to the service of the Altar. No tradition is recorded of its origin : but as it had been " for many centuries " in the same possession, everything leads to the belief that it found its way to Vienna after the Frankish conquest of Constan­tinople, when so many grand Camei became dispersed throughout Europe. The existence of such a natural pro­digy as a slab of Agate of the dimensions this patera de­manded renders the vast prices given for similar rarities under the Csesars no longer a thing to be wondered at. The shape of this dish is precisely that of the tralla, and of the class of vessels more peculiarly formed out of the Murrhine-stone, as its natural capabilities dictated. The Emperor * Adding, ''Though, man be silent, the very stones proclaim the glory of God ! "