The press and police have been condemned for the way they fall on mere rumour and plaster it across the headlines, Sir Edward Heath’s ‘paedophilia’ being the latest example. The Roman historian Tacitus (c. ad 56–118) well understood the phenomenon.

‘Rumour is not always wrong; it is sometimes correct,’ Tacitus asserts, well aware that the occasional accurate rumour reinforced the potential credibility of the many false ones; and he understood why they played such a part in the world of the emperors, ‘where men’s throats were slit with a whisper’ (Juvenal).

His historical point was the contrast between the freedom of information that he believed Romans enjoyed under the republic, and the deprivation of information and liberty that prevailed in the closed, secretive courts of the emperors. Since, under those conditions, people had to rely on rumour to understand events, he was simply describing accurately what life was like in imperial Rome. Some rumours, it is true, Tacitus reported only to refute, at once or later; but others he left hanging, creating the sense of a murky, unstable world, in which appearance and reality were difficult to tell apart.

But rumour served another purpose. Ancient historians believed that it was human motives and intentions that drove affairs. So whether the rumours were true or false was in a sense irrelevant; as long as rumours existed, they had an influence on the mindset, and therefore the actions, of those affected by them. One has only to read Tacitus’ portrayal of the hag-ridden emperor Tiberius (d. ad 37) to understand why he ended up a paranoid wreck.

We like to believe we live in an open society, where things are not swept under the carpet. So when rumour suggests they have been, the press inevitably reacts as it does; for we feel about these matters as Tacitus did. By the same token, mere rumour puts the police in a difficult situation: react, to invite public evidence, and they are sensation-mongers; refuse to react, or do so secretly, and they are part of the cover-up. All very Tacitean.