The two accounts given by Geoffrey Malaterra and William of Puglia of Robert Guiscard's expedition to the Balkans (siege of Durazzo, battle against Alexis Commene - 1081-1082) are two different readings of the same facts. The article is less interested in the events themselves than in the choices of writing or rewriting of the two authors to give an account of them in the respect of the chosen genre - historiographical narrative for the first and epic for the second - and of the general understanding they had of past events in the service of the Hauteville, their patron.