This study is an examination of the historiography of the ancient-medieval texts that record events related to the Northumbrian and the Pictish royal houses in the seventh century. The Picts, the Scots and the Celtic Britons fell into subjugation under the control of the expansionist Northumbrian kings and remained there for most of the seventh century. Northumbrian expansion was halted by Bridei, king of the picts, when he put down the advancing Northumbrian forces of king Ecgfrith at the Battle of Dunnichen, also known as Nechtansmere, in the year A.D. 685. The outcome of the battle not only stopped Northumbrian expansion to the north, but began its reversal. The battle also allowed the Picts to gain back the lands they had lost to their Northumbrian enemy. For the Northumbrians, the battle had political and ecclesiastical implications that may have contributed to the later decline of their kingdom.