The Battle of Dun Nechtain is fought between a Pictish army under King Bridei III and the invading Northumbrians under King Ecgfrith, who are decisively defeated.
The Battle of Dun Nechtain or Battle of Nechtansmere (Scottish Gaelic: Blàr Dhùn Neachdain, Old Irish: Dún Nechtain, Old Welsh: Gueith Linn Garan, Modern Welsh: Gwaith Llyn Garan, Old English: Nechtansmere) was fought between the Picts, led by King Bridei Mac Bili, and the Northumbrians, led by King Ecgfrith, on 20 May 685.
The Northumbrian hegemony over northern Britain, won by Ecgfrith's predecessors, had begun to disintegrate. Several of Northumbria's subject nations had rebelled in recent years, leading to a number of large-scale battles against the Picts, Mercians and Irish, with varied success. After sieges of neighbouring territories carried out by the Picts, Ecgfrith led his forces against them, despite advice to the contrary, in an effort to reassert his suzerainty over the Pictish nations.
A feigned retreat by the Picts drew the Northumbrians into an ambush at Dun Nechtain near the lake of Linn Garan. The battle site has long been thought to have been near the present-day village of Dunnichen in Angus. Recent research, however, has suggested a more northerly location near Dunachton, on the shores of Loch Insh in Badenoch and Strathspey.
The battle ended with a decisive Pictish victory which severely weakened Northumbria's power in northern Britain. Ecgfrith was killed in battle, along with the greater part of his army. The Pictish victory marked their independence from Northumbria, who never regained their dominance in the north.