I have now run through the principal varieties of Roman glass, and the order in which I have arranged the different classes—the inlaid and millefiori first, then the moulded, the blown, and finally, the cut and engraved glass—is in a measure a chronological one, following roughly the order in which these various methods of working and styles of decoration succeeded one another, or rather were dominant, in successive ages. I will end this chapter with a few notes concerning the methods of preparation and the geographical distribution of Roman glass. As far as contemporary evidence goes, all our information on the first head is derived from the brief and very unsatisfactory statements of Pliny. There is, however, every reason to believe that there were few important changes in the construction of the furnaces, or in the preparation of the materials, during the time that intervened between, say, the fourth century of our era and the period in the Middle Ages with regard to which we have further sources of information. That is to say, we may regard the comparatively adequate account of the manufacture of glass given by the monk Theophilus, and by the pseudo-Heraclius,[44] as on the whole applicable to Roman times. Even at the present day at Murano, and doubtless at other glass-works little affected by modern industrial processes, much of the old method of working and many of the old terms remain almost unchanged. To give but one example:—when the workman is preparing the half-liquid gathering or ball of glass at the end of his blowing-tube, previous to inflating it with his breath to form the _paraison_ or vesicle, he trundles the viscous mass upon a slab of iron which rests on the ground beside his furnace. This iron slab is known as the ‘marver’—there are similar names for it in other European languages—and it is always understood that the plate in question was formerly made of marble. So, no doubt, it may have been at some remote period, but we find that the pseudo-Heraclius, describing in the twelfth century or thereabouts the manufacture of glass, speaks of this same plate as ‘_tabula ferri quæ marmor vocatur_.’ Perhaps we should have to go back to the stone slab on which the Egyptian glass was rolled to find the origin of this ‘marver.’[45]