Of the three principal branches of ancient art, that of which we know least is painting, properly speaking; the art of Polygnotus, of Zeuxis, and of Apelles. Of this we have but few remains, and we are obliged to take our ideas of its excellence from the descriptions of ancient authors. We have indeed the wall-paintings of those Campanian cities which were so long buried under the ashes of Vesuvius; paintings which were uncovered in great numbers under the Napoleonic domination, and have in later times been added to every year, in spite of the indolent fashion in which the excavations have been conducted. Fragmentary mural paintings of the same kind have also been discovered in Rome and in a few other neighbourhoods. But after all, great though the interest may be which attaches to these works, it must not be forgotten that they are Italian rather than Greek, that they are the decorations for the most part of small provincial cities, and that even the best of them, when compared with the productions of the fifth and fourth centuries before our era, are examples of decadence. At the most they enable us to recall, with some approach to probable truth, the taste and technical methods of the Alexandrian school.[17] Winckelmann and his immediate successors saw the ashes cleared from the first Pompeian wall-paintings. But they possessed no standards by which they could define the styles of those great schools of painting which flourished in Greece between the epoch of the Persian Wars and the beginning of the Macedonian supremacy; such a definition we may now however attempt with at least partial success. Since the time of Winckelmann hundreds and thousands of those painted vases of burnt clay, which the public persist in calling Etruscan, have been discovered, classified, described, and explained, in such a manner as to leave unsolved scarcely any of the problems upon which they could cast a light. [17] See upon this subject M. Wolfgang Helbig's _Untersuchungen ueber die Campanische Wandmalerei_. Leipsic, 1873. M. Boissier has summed up the leading opinions in this matter in an interesting article in the _Révue des Deux Mondes_, entitled _Les Peintures d'Herculaneum et de Pompéi_ (October 1, 1879).