þæs ymb .iiii. niht Æþered Cyning 7 ælfred his
broþur þær micle fierd to Readingum gelæddon 7 wiþ
þone here gefuhton. 7 þær wæs micel wæl geslægen
on gehwæþre hond, 7 Æþelwulf Aldormon wearþ ofslægen,
7 þa Deniscan ahton wælstowe gewald. 7 þæs ymb .iiii.
niht gefeaht Æþered Cyning 7 Ælfred his broþur wiþ
alne þone here on Æscesdune, 7 hie wærun on twæm gefylcum:
on oþrum wæs Bachsecg 7 Halfdene þa hæþnan cyningas,
7 on oþrum wæron þa eorlas. 7 þa gefeaht se cyning æþered
wiþ þara cyninga getruman, 7 þær wearþ se cyning
Bagsecg ofslægen.
From the Anglo-Saxon Chronicle entry for 871:
Then four nights afterward king Athelred and Alfred his brother led a great
army there into Reading and fought against the army [of the Danes]. And there
was great slaughter on either hand, and Athelwulf the Ealdorman was slain, and
the Danes had control over the place of slaughter. And after four nights King
Athelred and Alfred his brother fought against the entire army at Ashdown, and
they were in two groups: in the one was Bagsecg and Halfdane, the heathen kings,
and in the other were the [Danish] earls. And then King Athelred fought against
the troop of the kings, and there was King Bagsecg slain.