A certain politician's wallpaper, the extra-marital affairs of Ministers, the meaning of William Hague's baseball cap: articles of this ilk seem to take up column feet each year, and biography sections of bookshops get bigger every year. If you thought that analysing the private lives of public figures was a modern phenomenon, think again. Suetonius, Lives of the Caesars (on which I, Claudius is partly based) shows that there were similar obsessions almost two millennia ago. Catharine Edwards, translator of the Oxford World's Classics edition published this autumn, reports:

Suetonius' Lives of the Caesars, starting with Julius Caesar and ending with the emperor Domitian, has always had its place as a fund of extraordinary tales of imperial vice - and, at times, of models of imperial virtue. Suetonius presents us with shocking accounts of Caligula's plan to make his horse consul and of Nero singing while Rome burned, as well as with edifying descriptions of Augustus' splendid redevelopment of the city of Rome and Titus' decision to put the state before his love for Berenice. Centuries later rulers might aspire to being hailed as another Augustus or Titus - and dread being labelled another Caligula or Nero.

Suetonius held a succession of posts at court, including a period in charge of imperial correspondence under the emperor Hadrian. These were highly influential positions which gave him close access to the emperor - and to a wealth of fascinating documentary material such as the letters of Augustus, from which he quotes extensively. Suetonius offers little in the way of chronological narrative and it would be rash to rely on the factual accuracy of the stories he tells about the Caesars. But what he has to say about the eccentricities and achievements of emperors, their virtues and vices, gives us a valuable insight into ancient Roman debates about imperial power and how it should be exercised.

Many of the virtues and vices Suetonius describes relate clearly to an emperor's public role. But Suetonius is also notorious for the space he devotes to his subjects' sex lives. While details of what we might describe as 'private life' often appear in the later sections of the Lives, thus in a sense separate from emperors' public activities, Suetonius hardly characterizes such material as 'private'. Romans traditionally viewed the personal lives of public figures as a legitimate public concern (a view shared today at least by the editors of tabloid newspapers). For Romans, a public figure revealed a huge amount about himself: by the way he chose to decorate his house - Augustus' simple residence makes clear he has no aspirations to tyranny; his style of dress - Julius Caesar's ungirt tunic reflects his unbounded appetite for power; and his eating habits - Claudius' habit of eating at the wrong time is a telling symptom of a more general failure to grasp what was appropriate behaviour for a ruler. Some practices deemed reprehensible for public figures in the modern world appear, however, to have provoked little criticism. Augustus' affairs with young girls seem to have been viewed as an acceptable indulgence of masculine appetite.

Suetonius aims to give his readers insights into the characters of individual Caesars through a wide variety of means, including, for instance, descriptions of their physical appearance (thought by ancient physiognomists to be a clear index of character). All the same, it is highly significant that Suetonius almost never seems to be concerned with why emperors were the way they were. This is one of the most striking ways in which Suetonius' 'biographies' are quite unlike modern works of biography. Following the trend established by Lytton Strachey's Eminent Victorians (1918), modern biographers have generally sought to explain their subjects' characters. More often than not the subject's sexuality is presented as the key to his or her character. Of course sexual behaviour has an important part to play in Suetonius' Lives. For many readers, Tiberius disporting himself in the swimming pool with little children, or Caligula treating senators' wives as if they were slave girls, are among the most memorable episodes. But these stories are not presented by Suetonius as having a key explanatory role. Rather sexuality offers one more sphere in which emperors may be judged and compared. Today, of course, the accounts of politician's sexual proclivities are reported and judged somewhat differently.