Some persons have considered the paintings found at Herculaneum and Pompeii to be frescoes; nevertheless Winckelmann, who is an authority in these matters, said, a hundred years ago, in speaking of those works, “It is to be remarked that the greater part of these pictures were not painted on damp lime, but upon a dry ground, which is rendered very evident by several of the figures having scaled off in such a way as to show distinctly the ground upon which they rest.” The whole mistake has arisen from taking the expression “_in udo pariete_,” found in Pliny, in too literal a sense; the error, which might at all events have been dissipated by an attentive examination of the examples themselves, would not have lasted long if the passage from Pliny had been compared with a statement of Vitruvius, which informs us that they applied to fresh walls uniform tints of black, blue, yellow, or red, which were destined to form the grounds of paintings, or even allowed them to remain plain, like our present coloured walls. The employment of this process may also be easily recognised in the paintings of Pompeii, where this uniform colouring has sometimes penetrated nearly an inch into the stucco of the wall. On this ground, when it was perfectly dry, ornamental subjects were painted either in distemper or encaustic. Thus, therefore, it is shown that the process of painting _in fresco_ was unknown to the ancients, and was invented by artists of succeeding times; but it would be difficult to assign any precise date to this invention; for however far we go back, we do not find any authors who fix the epoch at which the new method was for the first time followed. We are, therefore, compelled to notice the age of some particular example which shows that the discovery had then taken place, without being able to determine the exact date of its commencement.