By progressive improvements, which were made especially when the manufacture came into the hands of the Roman artists, this Egyptian paper was at length brought to a high degree of perfection. In later ages it was made of considerable thickness--perfect whiteness, and an entire continuity and smoothness of surface. Nevertheless, it was, at the best, so friable, that when durability was required, the copyists inserted a page of parchment between every five or six pages of the papyrus. Thus the firmness of the one substance defended the brittleness of the other; and great numbers of books, constituted in this manner, have resisted the accidents and decays of twelve centuries. Three hundred years before the Christian era, the commerce in the paper of Egypt had extended over most parts of the civilised world; and long afterwards it continued to be a principal source of wealth to the Egyptians. But at length the invention of another material, and also that interruption of commerce which ensued in consequence of the conquest of Egypt by the Saracens, banished the Egyptian paper from common use. Comparatively few manuscripts on this material are found of later date than the eighth or ninth century; although it continued to be occasionally used long afterwards. The charta bombycina, or cotton paper, which has often improperly been called _silk_ paper, had unquestionably been manufactured in the East as early as the ninth century, and probably much earlier; and in the tenth century it came into general use throughout Europe. Not long afterwards, this invention was made still more available for general purposes by the substitution of old linen, or cotton rags, for the raw material; for by this means both the price of the article was reduced, and its quality greatly improved. The cotton paper manufactured in the ancient mode is still used in the East, and is a beautiful fabric; it is also extensively used in the United States. From this account of the materials successively employed for books, it will be obvious, that a knowledge of the changes which these several manufactures underwent from age to age, will often make it easy, and especially when employed in subservience to other evidence, to fix with certainty the date of manuscripts; or at the least, to furnish infallible means for detecting fabricated documents.