The two candidates for the location of this Battle are either The River Glen in Northumberland, or the River Glen in Lincolnshire.
Yeavering Bell is a hillfort in Northumbria, near the town of Woller, overlooking the flat area where the River Glen flows into the River Till. The confluence of these two rivers has been identified as "the mouth of the River Glen." by some scholars. Excavations of the hillfort have shown that it was occupied in the time of Arthur, and he could have commanded his armies fighting the battle below.
The other candidate is the River Glen is in Lincolnshire, and many consider this the better possibility for the site of the battle. There were Angle settlements in this part of Britain, and Nennius cites four battles being fought in the Linnuis region, which many scholars believe to be Lincolnshire. The Glen in Lincolnshire seems more logical than the Glen in Northumbria, and ties in with the rest of Nennius's account.
The River Glen runs through southern Lincolnshire. The "mouth of the River Glen" in Nennius, could be the confluence of the river Glen with the River Welland, to the east of Surfleet, near Spalding.
The Battles of King Arthur