In 685 Ecgfrith, King of Northumbria, led an expedition against the Picts. North of the Tay, at Dunnichen near Forfar, he was slain and his army was destroyed by the forces of Brude mac Beli King of the Picts. The battle was fought near a loch, Symeon of Durham's ‘Nechtanesmere’, which scholars of the 19th century believed to have existed in the mosslands of Dunnichen. The site of the battle is not known, the loch itself has now disappeared, and the accounts of local historians and others, neither properly checked nor fully assimilated by national historians, are not all easily accessible. Floods which followed the winter of 1946–47 temporarily restored at least part of the old loch or mere, and in the summer of 1947 the flood-marks in the fields could still be seen. It seemed worth while to try to indicate on a map the extent of the vanished loch and this, with the aid of photography and a field-survey, has been possible. It seemed worth while also to sift the meagre scraps of evidence provided by chroniclers and, often unintentionally, by local writers of the last century, for these scattered scraps deserve to be brought together and re-examined.