According to the Anglo-Saxon Chronicle, Bagsecg and Healfdene (Norse Hálfdan) were joint commanders of the Great Army that invaded the Kingdom of Wessex during the northern winter of 870/71.
The Great Army is recorded as setting up camp at Reading and fighting the forces of Æthelred, King of Wessex, in several engagements during 871.
Likewise, other prehistoric sites in south central England, such as the Seven Barrows, have been erroneously regarded as memorials to those who fell at the Battle of Ashdown.
[35] However, a more general Scandinavian origin may be evident in the Chronicon Æthelweardi (late 10th century), which states that "the fleets of the tyrant Ingware (Norse Ivár) arrived in England from the north".
[55] One of the recorded engagements between Vikings and West Saxons was the Battle of Englefield, in which Æthelwulf, Ealdorman of Berkshire defeated a party of invaders led by several earls.
[56] It is possible that this conflict took place in the context of Bagsecg and Healfdene having the earls ride forth from Reading to forage, raid, and reconnoitre.
This time, the West Saxons confronted the Vikings at Reading, and were led by Æthelred, King of Wessex, and his younger brother, Alfred.
[58] Four days after the disaster at Reading, the West Saxons intercepted a massed force of Vikings at the Battle of Ashdown, fought somewhere in the Berkshire Downs.
One possibility is that the Vikings' recent victory at Reading had emboldened them to the extent that they intended to destroy the demoralised West Saxon army once and for all.
[64][note 4] The account of events preserved by Chronicon Æthelweardi,[74] as well as that dictated by Vita Alfredi, corroborate the identities of the Viking leadership, and reveal that the battle was particularly large, and particularly bloody, with thousands of casualties.
[75][note 5] The Anglo-Saxon Chronicle relates that fighting continued on into the night, suggesting that the West-Saxons indeed won a bloody and drawn-out affair.
[79] Although the Anglo-Saxon Chronicle and Chronicon Æthelweardi claim that the West Saxons fought the entire Great Army, it is unlikely that the Vikings left their encampment at Reading unprotected.
[116] As early as the eighteenth- and nineteenth centuries, Bagsecg has been associated with Wayland's Smithy,[101] a Neolithic long barrow,[117] erroneously assumed to have been erected as a memorial to him.
[101][note 10] Other prehistoric sites,[123] specifically the Seven Barrows in the region of Lambourn, have been mistakenly interpreted as memorials to the earls slain at the Battle of Ashdown.
[124] As early as the eighteenth- and nineteenth centuries,[125] the Uffington White Horse, dating to the Late Bronze Age,[126] has been incorrectly considered as an Anglo-Saxon memorial to Alfred and the victory at the Battle of Ashdown.