Perhaps we do not need to introduce Publius Cornelius Tacitus, who is considered by many to be the greatest Roman historian, one of the most important of all time. The "Annals," his most significant work, describes the history of the immediate successors of Augustus and the establishment of the new imperial system that he had founded, and they constitute our main historical source for that period. Their gravity becomes even greater as the author himself was an insider, with a successful political career that culminated in high offices. With the power of his rhetoric and the penetrating nature of his thoughts, Tacitus played a major role, mainly through the "Annals," in shaping the image we have today of the principles of the Roman Empire.

The first six books of the "Annals" describe the reign of Tiberius (14-37 AD) and are dominated by the presentation of his personality, which Tacitus was obsessed with. The passionate and detailed character sketch he portrays is considered the most memorable and penetrating depiction of an individual in all of antiquity and has been characterized as a 'miracle of art.' As a result of this obsession of the great historian, it is said that more contemporary books have been written about Tiberius than any other Roman Emperor.

The first three books describe the smooth transition of power to Tiberius after the death of the first Emperor, Augustus (a critical point for the consolidation of the imperial system) and the first, more positive part of his reign (until 22 AD). The last three books describe the second part of his reign, characterized by the Emperor's turn towards violence, until his death. An important role here is played by the rise of the all-powerful praetorian prefect Sejanus (his dramatic fall is described in a special appendix, as the relevant text of the "Annals" has been lost) and the voluntary isolation of Tiberius on Capri.