The deeds of King Olaf recorded in this story of his kinsman are therefore from the Norse "Saga of King Olaf the Holy," and the various incidents are assigned as nearly as may be to their place in the sequence of events given from the death of Swein to the accession of Cnut, in the contemporary Anglo-Saxon Chronicle, which is our most reliable authority for the period. The place where King Olaf fought his seventh battle, "Ringmereheath in Ulfkyl's land," is doubtful. To have localized it, therefore, on a traditional battlefield in Suffolk, where a mound and field names point to a severe forgotten fight in the line which a southern invader would take between Colchester and Sudbury, may be pardonable for the purposes of Redwald's story (Preface).
1989 work of Charles Watts Whistler, a writer of historic fiction, usually based on early English/Saxon chronicles, Norse or Danish Sagas and archeological discoveries.