Tacitus, the historian, is known to us chiefly from autobiographical touches in his own writings and from allusions in Pliny's letters. His full name is matter of doubt—Cornelius Tacitus being his nomen and cognomen; but whether his prænomen was Publius or Gaius can only be conjectured. Born perhaps at Rome (less probably at Terni) under the Emperor Claudius between 52 and 54 A.D., we infer that his family was respectable from his education, his profession, and his marriage. He studied rhetoric in Rome under M. Aper, Julius Secundus, and, likely enough, Quintilian; rose to eminence as a pleader at the Roman bar; and in 77 or 78 married the daughter of Agricola, the conqueror and governor of Britain. To this alliance he doubtless owed the accelerated promotion which, beginning with a quaestorship under Vespasian, made him prætor in 88 A.D. and a member of one of the priestly colleges. Next year he left Rome, probably for Germany, where, doubtless as governor, he must have acquired his knowledge of the features, natural and social, of the country; and he did not return till 93, when he found his father-in-law had recently died. We know him to have been an eye-witness of Domitian's reign of terror, almost blaming himself, as a senator, for complicity in that monster's judicial murders of such exemplary citizens as Helvidius and Senecio, and we have his own testimony as to the blessed change wrought by the accession of Nerva and Trajan. Under the former emperor he became consul suffectus, succeeding the great and good Virginius Rufus, on whom he delivered in the senate a splendid oraison funèbre. In 99 A.D., conjointly with the younger Pliny, he prosecuted the political malefactor, Marius Priscus, and the 'characteristic dignity' with which his share of the prosecution was conducted won him the thanks of the senate. After this we lose sight of him, but may assume it as certain that he saw the close of Trajan's reign, if not the opening of Hadrian's. The high reputation he enjoyed in life is attested by the eulogistic mention of him repeatedly made in Pliny's letters, and in the third century the Emperor Tacitus, proud to claim kinship with him, built in his honour a tomb which was still standing in the later decades of the 16th century, when it was destroyed by Pope Pius V. The same emperor also issued an edict by which the works of his namesake were to be copied out ten times yearly for presentation to as many public libraries.
In spite of this multiplication of copies we possess but a moiety of what he wrote. His earliest work, the Dialogus de Oratoribus, treats, in conversational form, of the decline of eloquence following on the change for the worse in the education of the Roman youth under the empire. This, published in 76 or 77, was for some time suspected to be from another pen, but is now included in every edition of his works. It has reached us entire. Next comes the Agricola, the literary character of which it is difficult to define. Quite a library has accumulated on the question whether it is a 'laudatio funebris,' or an 'apologia' written to shield the memory of Agricola from the charge of servility, or a historical panegyric framed for political ends. As biography it has grave defects, while it cannot be brought under any of the three above-named heads without serious deductions. But it will always be read for its elevation of style, its dramatic force, its invective and its pathos. For English readers its interest is unique. The third work, the Germania, or De situ, moribus, et populis Germaniae, is a monograph of the greatest value on the ethnography of Germany. Faulty in geographical detail, it becomes characteristically strong wherever human interest emerges. Fourth in order are the Historiae, or the history of the empire from the accession of Galba in 69 A.D. to the assassination of Domitian in 97. Of the twelve books originally composing it only the first four and a fragment of the fifth are extant. Tacitus is at his strongest in this narrative. His material was drawn from contemporary experience; and though the imperial archives were closed to him, he had at command the personal information open to a man of his position, to say nothing of correspondence (as of Pliny), the 'laudationes funebres,' the 'acta diurna' (what we should call the 'gazette'), and the 'acta Senatus,' the Roman equivalent for Hansard. He had no sympathy with the empire, as indeed we gather from his earliest work. He yearned for the return of an aristocratic oligarchy—the Rome of the Scipios and the Fabii. He is, on this account, a partisan, but is able to justify the most trenchant contrasts between the greatness of Republican and the deterioration of Imperial Rome, which latter he contrasts disadvantageously with the freedom and simplicity of even barbarian Germany. To his peculiar satirical gift which often makes him a 'Juvenal in prose' he gives free rein from time to time; though even in his bitterest moods he never forgets he is a Roman—a certain chauvinism betraying itself in his tendency to minimise the defeats of his compatriots and even the number of their slain. He had no appreciation of the higher qualities of the Jews, and his attitude to the growth of Christianity is that of a prejudiced, if cultured Roman, who, recognising an overruling providence or supreme 'Necessitas,' will not stoop to weigh the evidence to which the new religion appealed. The qualities conspicuous in the Historiae are maintained in his last work, the so-called Annales, a history of the Julian line from Tiberius to Nero (14 A.D. to 68). Of their sixteen books only eight have come down to us entire, four are fragmentary, and the others lost. In these, as in all his writings, his avowed aim was a noble one, to perpetuate virtue, and to stigmatisate baseness whether in word or deed. It is for its direct encouragement of the latter and persecution of the former that he constitutes himself so severe a censor of the imperial system; though he is not blind to the shortcomings of the later republic, under which the provinces, he admits, were worse off than under the empire. Among the more obvious defects which lower his value as a historian are his weakness in geography and his carelessness as to strategic details: he is, as Mommsen calls him, 'the most unmilitary of authors,' though Sallust or Livy run him hard. His style is the most strongly marked of antiquity—statuesque in outline, rich if somewhat too sombre in colouring, effective in antithesis, not seldom obscure from sheer condensation. But the more trouble the reader takes with it the greater his reward.
Editions: Orelli; Ritter; but best of all for the text, Halm; and for the interpretation, Nipperdey and Heräus. English editions are, of the Annals, by Frost, but especially that by Furneaux (2 vols. Oxford, 1883-91); of the Histories, by Spooner (1891); of the Germania, by Furneaux (1895), also by Stephenson and Davis. There is an admirable translation by Church and Brodribb. See also the short studies by Donne (1873), and Church and Brodribb (1881). M. Philippe Fabia in Les Sources de Tacite (1895) has sought to prove that Tacitus is overrated, that he makes bad omissions, and that he copies sentence after sentence from older authorities—in the Histories from Pliny the elder, in the Annals from Aufidius Bassus and Cluvius Rufus.