On 20 May 685, a Pictish force led by Bridei defeated a Northumbrian army led by King Ecgfrith at the Battle of Dun Nechtain, also known as Nechtansmere.

Ecgfrith was killed in the fighting. That made the battle more than a failed expedition. Northumbria was one of the strongest kingdoms in northern Britain, and Ecgfrith’s campaign showed how far its power had reached. The defeat showed where that reach could break.

The exact battlefield is uncertain. It is often linked to Dunnichen in Angus, though other locations have been proposed. The safer point is that Ecgfrith took his army into Pictish territory, somewhere in what is now Scotland, and did not come back.

This was not a battle between England and Scotland in the latter sense. The political map was still made up of kingdoms and peoples whose names do not fit neatly into modern borders: Northumbrians, Picts, Britons and others.

The result checked Northumbrian power in the north and helped secure Pictish independence from Northumbrian control. A king died, but the larger change was political. Northumbria had reached a hard limit.