The battle at Hatfield, usually taken as Hatfield Chase near Doncaster, is a historical might- have- been. It was at Hatfield in 633 that, in alliance with Penda of Mercia, Cadwallon of Gwynedd wiped out a Northumbria army under Edwin and for a year had the North at his mercy. Yet his defeat by Oswald near Hexham in late 634 destroyed for ever the dream of a Celtic reconquista in Britain. A dramatic turn of the tables has thus left Haethfelth as a footnote for historians, not a Chapter heading. But it was no small engagement. Since there has been disagreement on where it was fought (Yorkshire or Powys?) and when, this paper sets out discussion of it between 1860 and 2013, beside showing what its Welsh name, Meicen or Meigen, tells us on events.

Early observers well understood the magnitude of Cadwallon's triumph. In its entry for 630, Annales Cambriae (using North British sources) states ‘Battle of Meiceren (var. Meigen), and there Edwin was killed with his two sons. But Cadwallon was the victor.’ Plummer cited this (and Historia Brittonum, which names the sons as Osfrid and Eadfrid), giving the date as 633 and the place as Hatfield Chase, north- east of Doncaster. He did not reflect that the combat was surely south- east of the town, at the chase's southern edge, on the Roman road from Lincoln. He also quoted the Annals of Tigernach and Annals of Ulster on the event, which mention Edwin, Cadwallon and Penda, but not where they fought. On the aftermath of battle (dated to 633) Anderson quoted a Latin life of St Oswald by Reginald of Durham (active 1162– 73), with the statement on how Anfrid returned from Scottish exile to rule Bernicia for a year (while Edwin's son Osui took over Deira).

Full and careful information was given by Sir John Lloyd (1861– 1947), as expected. He observed that the ‘scene of this memorable encounter cannot, unfortunately, be fixed with certainty’. Bede implies somewhere in Deira or bordering it, but the Welsh called the spot Meicen, later identified with Meigen, near Breiddin Hill, north- east of Welshpool, Powys. Sensing confusion of two places with the same name, Lloyd opted for the northern location as site of the battle.