Laudator Temporis Acti

Andrew Wallace-Hadrill, Suetonius (London: Bristol Classical Paperbacks, 2004), p. 15 (footnote omitted):

Extraction of the relevant detail is Suetonius' characteristic method. Sometimes we get the impression of a large card-index system at work, reducing the sources to an endless series of one sentence items that can be reshuffled and redeployed at will. It would be interesting to know more about the technology behind the writing of the Caesars. We should pause before assuming that Suetonius actually had at his disposal anything so useful as a card-index. There is no evidence that antiquity had developed such systems. Scroll-form was normal for books; even library catalogues and the official records of imperial transactions were, to our knowledge, kept in scrolls rather than files. The philologist had to rely on a prodigious memory and much verbatim learning of texts in order to recall the passages where a given word occurred; naturally it also helped to be able to lean on those who had already done the donkey-work. The chances are that Suetonius worked from sources in scroll-form without the prop of an index and had to rely on memory to an extent no modern research student could expect to have to do. If there are imprecisions, errors and omissions in his material, this is a factor to be borne in mind.

Related post: Index System.