The city of Rome was founded, according to myth, in 753 BC. By the middle of the 2nd Century BC, it was the dominant power in the Mediterranean world; by the beginning of the 1st Century AD, its empire covered much of Europe, Western Asia and North Africa.
Among the tourist sites in modern Rome are the ruins of the Forum Romanum, the ceremonial heart of the city in the Julio-Claudian Age, and the Palatine, where the palaces of the Emperors were located. The forum includes the remains of many of the buildings that would have been familiar to Claudius, including the Temples of Vesta, Julius Caesar and Saturn, and the Curia Julia, one of several senate houses in Imperial Rome. Some of these are mentioned explicitly in the text of I, Claudius, and featured in the bookmarks. The Palatine ruins include the Domus Augusti, recently reopened following refurbishment, where Claudius lived during much of his life.
I, Claudius is set in the first half of the 1st Century AD and follows the fortunes of the Julio-Claudian dynasty, established by the Emperor Augustus, the adopted heir of Julius Caesar, in the aftermath of Caesar's assassination in 44 BC. The events of the book span the reigns of the following Emperors:
Augustus (27 BC - 14 AD)
Tiberius (14 AD - 37 AD)
Caligula (37 AD - 41 AD)
The Julio-Claudian dynasty included two other Emperors: Claudius himself (whose reign (41-54 AD) forms the subject of Graves's sequel, Claudius the God), and Nero (54-68 AD). Graves chose to begin I, Claudius with a Sibylline prophecy dramatically predicting key aspects of the five reigns, including Claudius's own. It was a feature of the dynasty that each Emperor was the adopted, rather than the natural, heir of his predecessor. Claudius was the exception, being nobody's intended successor but simply the member of the Imperial Family who happened to be at hand when, following the assassination of the insane Caligula, the palace guards were seeking a successor. There were many ironies in Claudius's life (not least the fact that he was a direct descendant not of Augustus, but of his defeated rival, Mark Antony) which provide much of the material for Graves's fiction.
Graves draws extensively on historical sources, notably Suetonius's The Twelve Caesars (written between 112 AD and 119 AD), which he translated himself; Tacitus's Annals (written between 100 AD and 116 AD); and Cassius Dio's Roman History (written between 200 AD and 230 AD). Whilst these writers almost certainly had access to written sources that did not survive into the modern era, some of their work, particularly that of Cassius Dio, also contains elements of fiction.