Editing Æthelred of Mercia (section)

==Relations with Northumbria==
Mercia had been in conflict with Northumbria since at least 633, when Penda of Mercia defeated and killed Edwin of Northumbria at the Battle of Hatfield Chase.<ref name=Yorke_78/>  However, there were diplomatic marriages between the two kingdoms: Æthelred's sister Cyneburh married [[Alhfrith of Deira|Alhfrith]], a son of Oswiu of Northumbria, and both Æthelred and his brother Peada married daughters of Oswiu.  Cyneburh's marriage to Alhfrith took place in the early 650s, and Peada's marriage, to Ealhflæd, followed shortly afterwards; Æthelred's marriage, to [[Osthryth]], is of unknown date but must have occurred before 679, since Bede mentions it in describing the [[Battle of the Trent]], which took place that year.<ref name=Kirby_93/><ref name=Kirby_117/><ref name=Bede_IV_21>Bede, ''Ecclesiastical History'', IV, 21, p.&nbsp;240.</ref>

Bede does not mention the cause of the battle, simply saying that it occurred in the ninth year of Ecgfrith's reign.  He is more informative on the outcome. [[Ælfwine of Deira|Ælfwine]], the young subking of Deira, was killed; Ælfwine was brother to Osthryth and Ecgfrith, and was well liked in both Mercia and Northumbria since Æthelred's marriage to Osthryth.  According to Bede, his death threatened to cause further strife between the two kingdoms, but Theodore, the Archbishop of Canterbury, intervened:<ref>This translation is by [[Leo Sherley-Price]], from Bede, ''Ecclesiastical History'', IV, 21, p.&nbsp;240; except that "Ecgfrith" has been substituted for "Egfrid" to keep the spelling consistent within this article.</ref><blockquote>Theodore, the beloved of God, enlisting God's help, smothered the flames of this awful peril by his wholesome advice.  As a result, peace was restored between the kings and peoples, and in lieu of further bloodshed the customary compensation was paid to King Ecgfrith for his brother's death.</blockquote>

Æthelred took possession of Lindsey again after the battle; the change in control this time was lasting, and Lindsey remained part of Mercia until the Viking invasion of the 9th century remade the map of England.<ref name=Kirby_117/><ref name=Bede_IV_12_225>Bede, ''Ecclesiastical History'', IV, 12, p.&nbsp;225.</ref> Conflict between Northumbria and Mercia did not completely cease after this date: Scottish annals record that [[Æthelbald of Mercia|Æthelbald]], an 8th-century Mercian king, ravaged Northumbrian territory in 740 while King [[Eadberht of Northumbria]] was absent fighting the [[Picts]].<ref>Anderson, ''Scottish Annals'', pp. 55–56.</ref> However, the Battle of the Trent effectively ended Northumbrian involvement in southern Britain.<ref>Stenton, ''Anglo-Saxon England'', p.&nbsp;85.</ref>

A conflict between Bishop [[Wilfrid]] of York and the church and secular establishment led to Wilfrid's expulsion from Northumbria and the division of his vast diocese, and Æthelred sided with Ecgfrith against Wilfrid.  After Ecgfrith's death in 685, Archbishop Theodore arranged a reconciliation between Wilfrid and [[Aldfrith of Northumbria|Aldfrith]], Ecgfrith's successor, but in 692 Aldfrith and Wilfrid fell out and Wilfrid went into exile in Mercia.<ref name=BEASE_474-6>Alan Thacker, "St Wilfrid", in Lapidge et al., "Blackwell Encyclopaedia of Anglo-Saxon England", pp.&nbsp;474–476.</ref><ref name=ODNB/> Æthelred now supported Wilfrid, making him bishop of the [[Middle Angles]], and defending him at the [[Council of Austerfield]] in about 702, when Wilfrid argued his case before an assembly of bishops led by Archbishop [[Berhtwald]] of Canterbury.<ref name=Kirby_126-7/><ref name=Stenton_143>Stenton, ''Anglo-Saxon England'', p.&nbsp;143.</ref> Æthelred's support for Wilfrid embroiled him in dispute with both Canterbury and Northumbria, and it is not clear what his motive was, though it may be relevant that some of Wilfrid's monasteries were in Mercian territory.<ref name=Kirby_126-7/>