the sons of Ragnar Lothbrok, to wreak revenge against Ælla of Northumbria who had supposedly executed Ragnar in 865 by throwing him in a snake pit, but the historicity of this explanation is unknown. According to the saga, Ivar did not overcome Ælla and sought reconciliation. He asked for only as much land as he could cover with an ox's hide and swore never to wage war against Ælla. Then Ivar cut the ox's hide into such fine strands that he could envelop a large fortress (in an older saga it was York and according to a younger saga it was London), which he could take as his own (compare the similar legendary ploy of Dido). Late the next year, the army turned north and invaded Northumbria, eventually capturing Ælla at York in 867. According to legend, Ælla was executed by Ivar and his brothers using the blood eagle, a ritual method of execution of debated historicity whereby the ribcage is opened from behind and the lungs are pulled out, forming a wing-like shape. Later in the year, the army moved south and invaded the kingdom of Mercia, capturing the town of Nottingham, where they spent the winter. King Burgred of Mercia responded by allying with the West Saxon king Æthelred of Wessex, and with a combined force they laid siege to the town. The Anglo-Saxons were unable to recapture the city, but a truce was agreed whereby the Danes would withdraw to York. The Great Heathen Army remained in York for over a year, gathering its strength for further assaults. Ivar and Ubba are identified as the commanders of the Danes when they returned to East Anglia in 869, and as the executioners of the East Anglian king, Edmund the Martyr, for refusing their demand that he renounce Christ. The precise account of Edmund's death is unknown, however it has been suggested that his capture and execution at the hands of the sons of Ragnar is likely to have occurred. Death The Anglo-Saxon chronicler Æthelweard records his death as 870. The Annals of Ulster describe the death of Ímar in 873. The death of Ímar is also recorded in the Fragmentary Annals of Ireland under the year 873. The identification of the king of Laithlind as Gothfraid (i.e., Ímar's father) was added by a copyist in the 17th century. In the original 11th-century manuscript, the subject of the entry