The oldest novel I can think of where alternate history has a major role is Orlando Furioso, published at the beginning of the XVIth century. If I remember corr

The oldest novel I can think of where alternate history has a major role is Orlando Furioso, published at the beginning of the XVIth century. If I remember correctly, the first scene is a battle were Charlemagne's army is beaten by a Saracen army. Later on, the Saracens lay siege to Paris. The world is mostly realistic, with an alternate history and elements of fantasy (griffons, magic spells). Orlando is much more than an uchronia, it is poetic, epic, fantastic, funny and sometimes morally challenging. This wonderful book is not mentioned on the page "Oldest" of this site where the oldest novel was published in 1732.