Snorri Sturluson's History of the Kings of Norway, usually known as Heimskringla, is an important source of information about events in Scandinavia during the period covered by this book. It is also valuable for an understanding of some events in England. Its value to students of English history has been diminished by a difficulty in aligning some events, associated with the Heimskringla hero, St Olaf, with the chronology of events recorded in the Anglo-Saxon Chronicle (ASC). This difficulty has led some historians to interpret the Heimskringla sources in a manner that the present writer questions.

Professor Campbell was a very influential critic who agreed that Snorri's interpretation of his skaldic verse evidence, concerning St Olaf's exploits in England, should be amended. Although Campbell was not the instigator of some of the revised interpretations of the evidence in Heimskringla, he explains them in appendix III of his edition and translation of the Encomium Emmae Reginae. It is convenient, therefore, to address the question, of whether Snorri's interpretation of events needed revision, by specific reference to Campbell's work. The chronological problem is best introduced in Campbell's own words: