Tacitus & Emperor Hadrian's Mutual Ancestry
Publius Cornelius Tacitus is considered one of the most reliable of all Roman historians. This means his passing reference to Jesus in Annals XV.44 is considered reliable and genuine. However, from the data above it appears that Tacitus the historian was a blood relation of Emperor Hadrian, through Domitia Paulina I. Julius Calpurnius Piso (Severus/Servianus), of whom evidence points to being the author of the Book of Revelation, was a son of Arrius Calpumius Piso, known in history as Flavius Josephus. Julius was the brother-in-law of Emperor Hadrian, so Julius' daughter, Julia Severiana Paulina, was a niece of Emperor Hadrian. Julius Piso's daughter, Julia, was a descendant of Augustus Caesar through her mother Domitia Paulina II, who was Emperor Hadrian's sister. But Tacitus the historian was related to the Piso family through the marriage of his son, Pedanius Fuscus, to Julius Piso's daughter, Julia. (Ref - Syme, "The Ummidii" (1968), p. 85)
Also, from the information above, we can see that Emperor Tacitus was indeed a descendant of Publius Cornelius Tacitus, as Emperor Tacitus was a son of Emperor Macrinus and nephew of Emperor Pescennius Niger. Emperor Tacitus' descent from the historian Tacitus is presented in the work the 'Historia Augusta'. Many scholars believe that the Historia Augusta is a work containing fraudulent information, and that would be correct, in a sense. Sir Ronald Syme once stated: The study of the HA continues to be dogged and bogged by retardatory scholarship. But enough. It remains to indicate, on short statement, the relevance and value of the bogus authors to the general theme.'
The Historia Augusta contains vital information regarding the relationships between the Roman Emperors. The Historia Augusta was written in a way that made it difficult for a researcher to understand if they did not know how to read it. The languages of the time were alpha-numeric, and royals were educated in all of them, so the royals could use a letter in exchange for another letter in another language that had the same number attached to it. They could also use letters that looked different in different languages, but were actually the same letter, for example, the letter R that we are familiar with looked like R in Latin, but in Greek, R looked like a P. So, ancient royalty could give names, but disguise them. A good example of that is the noble Roman lady Arria Piso, daughter of Arria the Younger, being called 'Fannia' in history, which is discussed here.
The world in which the Historia Augusta was written was one in which only royals could publish books, religious, historical, or poetic. Within their writings, royalty was recording their genealogies, but the way in which they gave the information meant that only their relatives and descendants would be able to read it. That is why many scholars have come to the conclusion that royal genealogies can only be traced back so far. The genealogies were given by creating names for various royal individuals, using nomenclature, acrostics, and abbreviations, but they were not just random names, they were created using parts of the names of ancestors and other relatives. Using initials of names was another method, as in the case mentioned above regarding the daughter of Arria the Younger being called 'Fannia'. The Pisos were related to the Flavians, so, the name 'Fannia' is actually F. Arria, or, Flavia Arria.