1911 Encyclopædia Britannica/Æthelred
ÆTHELRED, king of Mercia, succeeded his brother Wulfhere in A.D. 675. In 676 he ravaged Kent with fire and sword, destroying the monasteries and churches and taking Rochester. Æthelred married Osthryth, the sister of Ecgfrith, king of Northumbria, but in spite of this connexion a quarrel arose between the two kings, presumably over the possession of the province of Lindsey, which Ecgfrith had won back at the close of the reign of Wulfhere. In a battle on the banks of the Trent in 679, the king of Mercia was victorious and regained the province. Ælfwine, the brother of Ecgfrith, was slain on this occasion, but at the intervention of Theodore, archbishop of Canterbury, AEthelred agreed to pay a wergild for the Northumbrian prince and so prevented further hostilities. Osthryth was murdered in 697 and Æthelred abdicated in 704, choosing Coenred as his successor. He then became abbot of Bardney, and, according to Eddius, recommended Wilfrid to Coenred on his return from Rome. Æthelred died at Bardney in 716. (See Wilfred.)
Sources—Eddius, Vita Wilfridi (Raine), 23, 40, 43, 45-48, 57; Bede, Hist. Ecc. (ed. Plummer), iii. 11, iv. 12, 21; Saxon Chronicle, s.a. 676, 679, 704, 716.