Bede sometimes included in his theological books an acknowledgement of the predecessors on whose works he drew. In two cases he left instructions that his marginal notes, which gave the details of his sources, should be preserved by the copyist, and he may have originally added marginal comments about his sources to others of his works. Where he does not specify, it is still possible to identify books to which he must have had access by quotations that he uses. A full catalogue of the library available to Bede in the monastery cannot be reconstructed, but it is possible to tell, for example, that Bede was very familiar with the works of Virgil. There is little evidence that he had access to any other of the pagan Latin writers—he quotes many of these writers, but the quotes are almost found in the Latin grammars that were common in his day, one or more of which would certainly have been at the monastery. Another difficulty is that manuscripts of early writers were often incomplete: it is apparent that Bede had access to Pliny's "Encyclopedia", for example, but it seems that the version he had was missing book xviii, since he did not quote from it in his "De temporum ratione".