In his Historia Gotthorum (1655), Hugo Grotius set up a Swedish ‘Gothic myth’, a powerful historiographical construct aimed at increasing Swedish prestige by identifying the ancient Swedish as the forebears of the late antique Goths, Vandals and Lombards. Entering into dialogue with fellow historiographers was vital to this venture. The ‘Prolegomena’ to Historia Gotthorum are accordingly marked by an extensive polemical dimension. A critical discourse analysis of both explicit and hidden polemics in this text reveals a clever combination of scholarly argumentation on the basis of historical evidence and strategic image-building to convince the reader. Furthermore, Grotius regularly drew on the works of contemporary colleagues for his historical evidence. The present article sheds light on the various argumentation strategies deployed in the ‘Prolegomena’ to Historia Gotthorum and the role of early modern historiographical texts as treasure troves of historical knowledge. This not only offers further insight into Grotius’s historiographical practice, but also provides an excellent example of how early modern historical writers interacted with the texts of their immediate colleagues.