Due to confusion between the Don and the Sir-Daria in some ancient sources, Tacitus' account of the Roman campaign against Mithradates VIII of Bosporus might have been inspired by the episode of Alexander's crossing of the 'Tanais' reported by Quintus Curtius. Tacitus highlights the importance of the first Roman victory beyond this river: this land was considered the limit of the known world, as was also the case of Britannia, whose conquest was also described by Tacitus. If we admit a Claudian date for Curtius' work, the favourable image of Alexander's victory over the Sacae given by this author could have evoked the emperor's triumph over Mithradates, who was of Achaemenid descent.