§398. Size of the Rolls.--When a volume was consulted the roll was held in both hands and unrolled column by column with the right hand, while with the left the reader rolled up the part he was done with on the slip of wood fastened to the margin of the first sheet (Fig. 191). When he had finished reading he rolled it back upon the _umbilīcus_, usually holding it under the chin and turning the _cornua_ with both hands. In the case of a long roll this turning backward and forward took much time and patience and must have sadly soiled and damaged the roll itself. The early rolls were always long and heavy. There was theoretically no limit to the number of sheets that might be glued together, and consequently none to the size or length of the roll. It was made as long as was necessary to contain the given work. In ancient Egypt rolls were put together of more than fifty yards in length, and in early times rolls of approximate length were used in Greece and Rome. From the third century B.C., however, it had become customary to divide works of great length into two or more volumes, the division at first being purely arbitrary and made wherever it was convenient to end the roll, no matter how much the unity of thought was interrupted. A century later authors had begun to divide their works into convenient parts, each part having a unity of its own, such as the five "books" of Cicero's _Dē Fīnibus_, and to each of these parts or "books" was given a separate roll. An innovation so convenient and sensible quickly became the universal rule. It even worked backward, some ancient works being divided into books, which had not been so divided by their authors, e.g., Herodotus, Thucydides, and Naevius. About the same time, too, it became the custom to put the sheets upon the market already glued together, to the amount at least of the _scāpus_ (§394). It was, of course, much easier to glue two or three of these together, or to cut off the unused part of one, than to work with the separate sheets. The ready-made rolls, moreover, were put together in a most workmanlike manner. Even sheets of the same quality (§394) would vary slightly in toughness or finish, and the manufacturers of the roll were careful to put the very best sheets at the beginning, where the wear was the most severe, and to keep for the end the less perfect sheets, which might sometimes be cut off altogether.