In 685, against the advice of Cuthbert of Lindisfarne, Ecgfrith led a force against the Picts of Fortriu, who were led by his cousin Bridei mac Bili. On 20 May, Ecgfrith was slain at the age of 40, having been lured by a feigned flight to the mountains, at what is now called the Battle of Dun Nechtain, located at either Dunnichen in Angus or Dunachton in Badenoch. This defeat, in which most of Ecgfrith's army was lost, severely weakened Northumbrian power in the north and Bede dates the beginning of the decline of the kingdom of Northumbria from Ecgfrith's death and wrote that following Ecgfrith's death, "the hopes and strengths of the English realm began 'to waver and to slip backward ever lower'". The Northumbrians never regained the dominance of central Britain lost in 679; nor of northern Britain lost in 685. Nevertheless, Northumbria remained one of the most powerful states of Britain and Ireland well into the Viking Age. Ecgfrith was buried on Iona and succeeded by his illegitimate half-brother, Aldfrith.