Obedient to a now accepted principle of psychology, we follow in the development of our inquiry the sequence of evidences by which this subject has been established during the past generation. Postponing for the present any detailed account of the walled towns and groups of sculptures which have been the scene of recent investigation, we shall consider firstly those monuments which are found isolated and scattered throughout the regions indicated in the opening chapter. If, in so doing, we can yet be guided by the light of modern discoveries, we may hope to avoid some of the difficulties which beset the path of these pioneers whose work introduced to us this new material. Our method of study, like theirs, must be comparative; but we shall be content to confine ourselves almost entirely to the monuments identified as Hittite by the presence of the peculiar hieroglyphic signs or inscriptions carved upon them. It was indeed upon this line of evidence that Professor A. H. Sayce was enabled, thirty years ago, to establish the relationship of the unexplained inscriptions of Hamath with the sculptures of Kara-Bel in the far west of Asia Minor, and thence to make his brilliant inference of a forgotten empire.[127] We use the test of Hittite hieroglyphs, not only because it has become in this way fundamental to our subject, but because it is no longer open to doubt whether these peculiar signs are of Hittite origin or not. Formerly there may have been room for reasonable criticism so long as this conclusion was based only on the fact that these symbols were found chiefly on unexplained monuments from Hamath and neighbouring places in Northern Syria associated in history with the Hittites. But now the increasing accumulation of this kind of circumstantial evidence has been crowned by the discovery that the chief site of such monuments in Asia Minor, namely Boghaz-Keui, was for two centuries the capital of the Hittites, whose name (Hatti) appears freely on the literary documents that have been unearthed[128] there in recent excavations. Being secured then against fundamental error, a comparison of the Hittite monuments identified on this basis readily reveals peculiarities of art which may be regarded as typical, so that we might reasonably include in our category other monuments of like kind which lack only the ultimate criterion which we have set before us. We do not wish, however, nor do we need, in the scope of this volume, to press the argument by analogy, being warned against the pitfalls of such a method by several general considerations, and especially by the noticeable survival of Hittite influence in the local sculptures, like those of Phrygia[129] and western Lycaonia.[130]