"History is idle gossip about a happening whose truth is lost the instant it has taken place." - Gore Vidal
Five years ago today, Vidal died at the age of 86 from complications of pneumonia.
Of course, history is more than idle gossip. Also note that Vidal cited "history," not the notion of the discrete historical fact. After all, it's not merely idle gossip that Vidal did, in fact, die five years ago today. And the myriad resources of historical analysis in general don't all come down to so much idle gossip. Vidal was being provocative, as he often was.
Nonetheless, there's more than a little truth in what Vidal says here about history, depending on what kind of history is in question.
Especially regarding history of the pre-modern era, many sources include literal gossip and essentially report it as such. But it's also true that many things reported as fact in those eras cannot easily if ever be independently verified and might well have been just gossip. One thinks of some of the salacious details related in the works of Plutarch and Suetonius.
Probably, Vidal's larger point was that the truth of the past, including received, official history, can never be completely known. There is no omnipresent and omniscient historical recorder, something capturing forever every moment of human action on earth and the thoughts of those involved. Subjectivity and fading memories factor into the imperfection of the historical record and in part decide what is and isn't recorded in the first place.
More than likely, the subjectivity of history is something Vidal hoped to stress by very often relying on the first-person point of view in his historical novels, including an epistolary approach in Julian and using using diary entries like in Burr and transcription like in and Creation.