Tacitus

Tacitus was an ancient historian who wrote a history of Rome called Annals, which covered parts of Roman history including the Great Fire of Rome and the final years of Emperor Nero's reign. While Tacitus worked on the sections of Annals covering these events, he discovered documents written by the First Doctor, Ian Chesterton and others that radically altered his previous understanding of those events. Because of these discoveries, he had to delay completing his work to investigate the truth of the matter. The Keeper of Rome's Imperial Archives sent Tacitus a letter accusing him of breach of contract for the delay. Upset by the letter, he wrote back with an explanation and copies of the documents in question. The documents revealed not only that Rome had been visited by people from another time and space, but that in truth, Nero was not truly responsible for the fire. Tacitus was hesitant to reveal his finding publicly, on account of how the revelation that Nero's assumed guilt was a misunderstanding undermined the basis for all subsequent Emperor's claims. Rather than make the position of the current Emperor, Hadrian, legally unsound, Tacitus recommended the relevant papers be covered by the Imperial Secrets Act and not be released until 1987. As an alternative, he suggested if the Keeper of the Archives felt the truth should not be hidden, that Ascaris be recalled to Rome and made a scapegoat for the entire incident. (PROSE: The Romans)

The Fourth Doctor noted to Leonard de Vries that Tacitus had mentioned the Druids, but not in great detail. (TV: The Stones of Blood)