Before the second century B.C. the contents of Greek and Roman libraries were not books in the form to which we are accustomed, but rolls of papyrus, and the fittings of libraries were accordingly shelves with vertical divisions forming pigeon-holes, into which a roll or rolls were thrust. But the advantages of parchment as a material to bear writing were so obvious that the long rolls wrapped round a stick (_rotuli_) gave way gradually to the well-known form appropriate to parchment or paper, namely sewn and bound leaves (_codices_) either quarto—which was found at first to be the most convenient size—or folio or octavo. The receptacles in libraries (at Rome) were no longer pigeon-holes (_nidi_, _foruli_) or long narrow boxes (_loculamenta_), but undivided shelves (either fixed to the wall, _pegmata_, or standing against it, _plutei_). The wall space above these various forms of shelving was usually filled with decorative portraits or busts of great authors. Perhaps it is not accidental that in the great library collected by Sir Robert Cotton (now in the British Museum) the various parts were called (as they are still referred to) by the names of the Roman Emperors whose busts surmounted each division, and in the Bodleian, after the Civil War, the wall divisions of the Picture Gallery were surmounted by a series of ornamental medallions and portraits above the ordinary pictures on the walls. The books, whether disposed in regular book cases or in cupboards (_armaria_) with doors, were in Roman times laid on their side. [Sidenote: Mediæval Libraries.] The classical tradition concerning the care of books was apparently carried on with little change during the first five centuries of the Christian era. Ecclesiastical libraries were kept in churches, as classical libraries were usually connected with temples. It is usual to date the organization of mediæval collections from the Rule of St. Benedict in the sixth century; and the Order which he founded, with its direct offshoots, the Cluniacs, Carthusians and Cistercians, were foremost in assigning a place to literature in the daily duties of the monk. The gradual evolution of the library can be traced from the time when a few volumes could be accommodated in a press or presses in a recess or small room, usually at the north-east corner of the cloister near the chapter-house, to the fully developed collections of the fifteenth century, housed in a large separate room, which was almost always on the first floor, perhaps to avoid damp and to secure a good light. The following figures will illustrate the size of some considerable mediæval libraries in various places and times.