Stephen of Ripon wrote it down decades after the fact, and he was not aiming for restraint. According to his Vita Sancti Wilfrithi - the Life of Saint Wilfrid - the Picts who rose against Ecgfrith of Northumbria in 671 died in such numbers that their corpses filled two rivers, and the Northumbrian cavalry chased the survivors across dry stream-beds without ever getting their feet wet. The number is almost certainly an exaggeration, the kind of providential miracle that hagiographers liked to attach to favoured kings. But somewhere near the confluence of the Tay and the Earn, a Pictish rebellion against English overlordship was crushed in a single afternoon. The battle gave its name to no peace. Fourteen years later the Picts came back.
Through the seventh century, the kingdom of Northumbria expanded steadily northward from its heartland in what is now Yorkshire and Northumberland. The Annals of Tigernach record a siege of 'Etain' in 638 - generally taken to be the Northumbrian conquest of Eidyn, the British stronghold that the city of Edinburgh now occupies. With Eidyn fell the Gododdin territories south of the River Forth. Beyond the Forth lay the Picts, organized into the northern Kingdom of Fortriu and a 'Southern Pictish Zone' stretching down to the river. The Anglo-Saxon historian Bede, writing in the early eighth century, suggests that even the Picts had been subjugated by the Northumbrian king Oswald in the 630s and that this overlordship continued under his successor Oswiu. When Ecgfrith inherited the throne in 670, the empire was real but fragile.
Ecgfrith's kingdom, Stephen wrote, was 'weak' at his accession - the standard rhetorical setup before a great victory. In 671 word reached him that the Picts under Drest mac Donuel, king of Fortriu, were preparing to overthrow Northumbrian rule. Ecgfrith assembled an invasion force of cavalry and rode north. He was aided by a sub-king named Beornhæth, whom the historian James Fraser has tentatively identified as ruler of a southern Pictish kingdom called Niuduera, possibly located in what is now Fife. If that identification is right, the Northumbrian advance benefited from Pictish disunity: some southern Picts had thrown in their lot with the English and rode against their northern cousins.
Where exactly the two armies met is not recorded. One tentative suggestion places the battle on or near Moncreiffe Island in the Tay, just upstream of the confluence with the Earn - a strategic crossing point near the present village of Abernethy. Whether that identification holds depends partly on where the Kingdom of Fortriu actually was, a question modern scholarship has revised significantly by relocating Fortriu to the north of Scotland rather than the central belt. In Stephen's account, the Northumbrian cavalry was ambushed by a much larger Pictish force concealed in the landscape. The horsemen fought their way out and somehow turned the ambush into a rout. Pictish casualties, Stephen claimed, filled two rivers - hence the name historians have given the battle. The detail is almost certainly inflated.
The Northumbrian victory was decisive enough to break the Pictish rebellion. Stephen records that the surviving Picts were 'reduced to slavery and subject to the yoke of captivity' for the next fourteen years. The Irish annals of Ulster and Tigernach record that a 'Drost' was expelled from kingship in 671 - presumably the defeated Drest, deposed and replaced by Bridei mac Bili as a consequence of the failed revolt. The peace that followed was brittle. In 685, Bridei led another Pictish army against Ecgfrith at the Battle of Dun Nechtain. This time the Northumbrians lost. Ecgfrith himself was killed on the field, and the northward expansion of Northumbria ended for ever. The two rivers were full of the wrong dead, in the end. The Picts outlasted the empire that had drowned them.
The likely location of the Battle of Two Rivers is centred near 56.380 north, 3.422 west, in the area where the River Earn joins the River Tay, with Moncreiffe Island and the surroundings of Abernethy and Perth in view. From the air the confluence of the two rivers is the dominant feature: the Tay curving down from the north, the Earn coming in from the west, and the broad Strathearn valley opening between them. Best appreciated from 2,500 to 5,000 feet to take in the geography that may have shaped the seventh-century battle. Dundee Riverside (EGPN) lies roughly 15 nm east-northeast. Edinburgh (EGPH) is about 32 nm south.