Nestorchronik
Paul Bushkovitch form Yale University writes “the author was serving his rulers, identifying princes and people and leaving historians with a muddle virtually impossible to sort out.” He also mentions that there are discrepancies when overlapping Scandinavian history with the narrative of the "Primary Chronicle". For example, “archeological evidence does not fit the legends of the "Primary Chronicle”" such as: “in Scandinavia itself, there were no sagas of Viking triumphs and wars in Russia to match those recounting the conquest of Iceland and the British Isle’s”. The credibility of the Primary Chronicle should be taken with a grain of salt for its undertone of being a political tool to justify rule.