Battle of the Conwy In 877 they partitioned Mercia, taking the east for themselves and leaving the west to Ceolwulf. Gwynedd was also under attack from the Vikings, and in 877 King Rhodri Mawr was defeated and driven out. He returned the following year, but immediately came under attack from Mercia, which was still trying to maintain its hegemony in Wales. King Alfred's victory over the Vikings at the Battle of Edington in May 878 relieved the pressure on Mercia, and in the same year Mercia defeated and killed Rhodri Mawr. Ceolwulf died or was deposed in 879, and he was succeeded as Lord
Alfred the Great 22 January. They were defeated again on 22 March at the Battle of Merton (perhaps Marden in Wiltshire or Martin in Dorset). Æthelred died shortly afterwards on 23 April. In April 871 King Æthelred died and Alfred succeeded to the throne of Wessex and the burden of its defence, even though Æthelred left two under-age sons, Æthelhelm and Æthelwold. This was in accordance with the agreement that Æthelred and Alfred had made earlier that year in an assembly at "Swinbeorg". The brothers had agreed that whichever of them outlived the other would inherit the personal property that King Æthelwulf had