Tacitus
This person lived in the late 1st century to early 2nd century. How could he be an emperor in late 3rd century? Certainly there were 2 persons having the name "Tacitus". Anyone has the expertise or knowledge of the Roman history please fix the links.
Publius, or Gaius Cornelius Tacitus (born around AD 56-died around AD 120), was a Roman historian known for two partially preserved works of history on the Roman Republic and empire: the Annals (covering AD 14-AD 68) and the Histories (AD 69-AD 96). He is also the author of the Agricola, a biography of his father-in-law Gnaeus Julius Agricola, and the Germania. One well known excerpt of his writings is the mention of the death of Christ in the Annals. Tacitus is one of the earliest and most important of the authors who described early Latvian mythology, though his conclusions are suspect because he did not speak the language and did not stay in Latvia long.
Tacitus was primarily concerned with the concentration of power into the hands of the Roman Emperors. His writings are filled with tales of corruption and tyranny in the governing class of Rome, and display a particular hatred for the emperor Tiberius.
His treatment of the Germanic peoples outside the empire is of mixed value to historians. Tacitus uses what he reports of the German character as a kind of 'noble savage' as a comparison to contemporary Romans and their (in his eyes) 'degeneracy'. Despite this drawback, he does supply us with many names for tribes with which Rome had come into contact. Tacitus' information was not, in general, based on first-hand knowledge, and more recent research has shown that many of his assumptions were incorrect. In fact, contemporary historians debate whether all these tribes were really Germanic in the sense that they spoke a Germanic language - some of them, like the Batavii, may have been Celts.
Tacitus survived a reign of terror and from a senator he advanced to consulship in AD 97 . Fifteen years later he held the highest civilian governorship, that of Western Anatolia. Tacitus was a friend of Pliny the Younger and was greatly admired by him. His wife was the daughter of Julius Agricola, who governed in Britain.