Background and structure
The Annals was Tacitus' final work and provides a key source for modern understanding of the history of the Roman Empire from the beginning of the reign of Tiberius in AD 14 to the end of the reign of Nero, in AD 68. Tacitus wrote the Annals in at least 16 books, but books 7–10 and parts of books 5, 6, 11 and 16 are missing.
The period covered by the Histories (written before the Annals) starts at the beginning of the year AD 69, i.e. six months after the death of Nero and continues to the death of Domitian in 96. It is not known when Tacitus began writing the Annals, but he was well into writing it by AD 116. Modern scholars believe that as a senator, Tacitus had access to Acta Senatus, the Roman senate's records, thus providing a solid basis for his work.
Together the Histories and the Annals amounted to 30 books. These thirty books are referred to by Saint Jerome, and about half of them have survived. Although some scholars differ on how to assign the books to each work, traditionally fourteen are assigned to Histories and sixteen to the Annals. Tacitus' friend Pliny referred to "your histories" when writing to him about his earlier work. Although Tacitus refers to part of his work as "my annals", the title of the work Annals used today was not assigned by Tacitus himself, but derives from its year-by-year structure.
Of the sixteen books in Annals, the reign of Tiberius takes up six books, of which only Book 5 is missing. These books are neatly divided into two sets of three, corresponding to the change in the nature of the political climate during the period.
The next six books are devoted to the reigns of Caligula and Claudius. Books 7 through 10 are missing. Books 11 & 12 cover the period from the treachery of Messalina to the end of Claudius' reign.
The final four books cover the reign of Nero and Book 16 cuts off in the middle of the year AD 66. This leaves the material that would have covered the final two years of Nero's reign lost.