Writers of historical fiction must read history. I read of the Roman generals, the Scipios, father and son, in Poul Anderson's "Delenda Est." While "studying"/suffering Latin at school, I found that I was translating a sentence about the younger Scipio saving his father's life at the battle of Ticinus. I reflected that, unknown to the historians, Time Patrolman Manse Everard was nearby at Ticinus.
Neil Gaiman's "August," about the Emperor Augustus, is presented as extracts from the memoirs of the dwarf, Lycius. Gaiman's source was Robert Graves' translation of Suetonius' The Twelve Caesars which confirms the historicity of Lycius as depicted in "August," although we must assume that the dwarf's memoirs relating the real reason for the decline of Rome have not survived...
Authors of fiction write in the cracks of history.