After this summary of the Clontarf episode in Njals saga, and before proceeding farther, it needs to be pointed out that the main points in Njals saga agree with contemporary and near-contemporary Irish sources.
A genuine folk remembrance specifically about Clontarf is the poem Darradarljod, which immediately follows the account of the battle in Njals saga and is introduced as a supernatural report of the conflict.
26) While Njals saga portrays Clontarf as a disaster for the Vikings--as do the Irish sources--Darradarljod sees it, reasonably, as not being entirely without benefits for the Irish Vikings, who might have been relieved to see both their Irish and Viking rivals decimated.
Porsteins saga has a brief account that follows the main points of the story in Njals saga.
Except for dating the Battle of Clontarf inaccurately to the fifth year after the Battle of Svold, all the information in Orkneyinga saga is found in Njals saga.
What has not been noted is that the common items of information about Sigurdr's participation in the Battle of Clontarf are presented in identical order in Orkneyinga saga and Njals saga.
The banner incident, which is found in Orkneyinga saga, Njals saga, and Porsteins saga, is illuminating.
Less easy to explain as authorial selection and more suggestive of borrowing are the British or Irish place names in Njals saga (chs 85-6, 89 and 153-7).
Some names found in both Njals saga and Orkneyinga saga--such as Katanes (Caithness) and Dyflinn (Dublin)--are commonplace and found in numerous Icelandic texts.
Several place names in Njals saga suggest that the author was adapting material also found in Orkneyinga saga to fit his story.
The three British or Irish place names found in Njals saga but not in Orkneyinga saga--Kola, Kantaraborg, and Hvitsborg--reinforce the suspicion that its author was borrowing material from several works rather than following a single record.
The second name, Kantaraborg, is given in Njals saga as the capital of the Irish high king Brian.