The westward progress of the Northumbrians is later and much more historical.  Theodoric, son of Ida, as we may perhaps infer from the old Welsh ballads, fought long and not always successfully with Urien of Strathclyde.  But in 592, says Baeda, who lived himself but three-quarters of a century later than the event he describes, “there reigned over the kingdom of the Northumbrians a most brave and ambitious king, AEthelfrith, who, more than all other nobles of the English, wasted the race of the Britons; for no one of our kings, no one of our chieftains, has rendered more of their lands either tributary to or an integral part of the English territories, whether by subjugating or expatriating the natives.”  In 606 AEthelfrith rounded the Peakland, now known as Derbyshire, and marched from the upper Trent upon the Roman city of Chester.  There “he made a terrible slaughter of the perfidious race.”  Over two thousand Welsh monks from the monastery of Bangor Iscoed were slain by the heathen invader; but Baeda explains that AEthelfrith put them to death because they prayed against him; a sentence which strongly suggests the idea that the English did not usually kill non-combatant Welshmen.

The victory of Chester divided the Welsh power in the north as that of Deorham had divided it in the south.  Henceforward, the Northumbrians bore rule from sea to sea, from the mouth of the Humber to the mouths of the Mersey and the Dee.  AEthelfrith even kept up a rude navy in the Irish Sea.  Thus the Welsh nationality was broken up into three separate and weak divisions—­Strathclyde in the north, Wales in the centre, and Damnonia, or Cornwall, in the south.  Against these three fragments the English presented an unbroken and aggressive front, Northumbria standing over against Strathclyde, Mercia steadily pushing its way along the upper valley of the Severn against North Wales, and Wessex advancing in the south against South Wales and the West Welsh of Somerset, Devon, and Cornwall.  Thus the conquest of the interior was practically complete.  There still remained, it is true, the subjugation of the west; but the west was brought under the English over-lordship by slow degrees, and in a very different manner from the east and the south coast, or even the central belt.  Cornwall finally yielded under AEthelstan; Strathclyde was gradually absorbed by the English in the south and the Scottish kingdom on the north; and the last remnant of Wales only succumbed to the intruders under the rule of the Angevin Edward I.

There were, in fact, three epochs of English extension in Britain.  The first epoch was one of colonisation on the coasts and along the valleys of the eastward rivers.  The second epoch was one of conquest and partial settlement in the central plateau and the westward basins.  The third epoch was one of merely political subjugation in the western mountain regions.  The proofs of these assertions we must examine at length in the succeeding chapter.