Fabia (1893), Questa (1967), Devillers (2003) and others who have written monographs on Tacitus’ sources for the Annals based their conclusions on inconsistent selection criteria and incomplete sampling. This paper offers the first full inventory of the sources Tacitus cited and, based on statistical analysis of when and for what purpose he deployed citations, offers some conclusions about his need for documents, such as decrees, relative to his need for non-documentary sources, such as named authors.
The paper first outlines selection criteria for identifying citations and assigning them to the following categories: letters, decrees, oral history (e.g. tradunt plerique), anonymous writers, named writers, edicts, laws, inscriptions, unknowns, acta diurna and acta senatus. In all Tacitus cites 462 sources in the Annals. Next, the paper sketches what may be learned by examining the citation incidence rate per 1000 lines in a) the entire Annals (macro analysis) and b) within particular narrative types such as domestic affairs, foreign affairs, and palace life (micro analysis).
Macro analysis of each narrative year shows a direct correlation between the number of lines devoted to senatorial narratives and the increase or decrease of cited documentary sources. A chi-square test confirms with overwhelming likelihood that this relationship is coincidental (p = 9.399 x 10-15), meaning it is extremely unlikely that Tacitus artfully constructed this correlation in order to mislead his readers. Moreover, in senatorial narratives, documentary sources appear in 73% greater density than do non-documentary sources. This trend, of which Tacitus would have been unaware, is constant throughout the Annals (± 3% for each of Ann. I-VI, XI-XII and XIII-XVI). This means that whenever Tacitus wrote about the senate for a particular narrative year, whether he wrote little or a lot, his need for decrees and other documents consistently outweighed his need for non-documentary sources.
Macro analysis shows that Tacitus deployed non-documentary sources to reinforce themes throughout the Annals: a) the senate’s servility in Ann. I-VI, b) the marginalization of the senate in Ann. XI-XII and c) the final transference of senatorial authority to the palace in Ann. XIII-XVI. Revealed is what an impoverished picture of the early empire Tacitus would have left us, had he consigned himself to using non-documentary sources alone. This paper lays the groundwork for a larger study of Tacitus' research and offers a method for evaluating other ancient historians' use of citations.