King Athelstan established the River Wye as a boundary in this region.
Descriptive answer acceptableIn 2008, Mark Roberts' attempt to establish a lordship around Trellech in this region was denied by the courts. Lords in this region had the unique right to construct castles; unsurprisingly, this region contains the densest concentration of motte and bailey castles in its country. King Athelstan established the River Wye as a boundary in this region. William I gave the earldoms of Hereford, Shrewsbury, and (*) Chester to some of his most reliable men because of the defensive importance of this region. The western border of Mercia set the location of this region for the next several hundred years, perhaps most visibly at Offa's Dike. For 10 points, name this ill-defined region on the border of England and a Celtic region to the west.
Descriptive answer acceptableIn 2008, Mark Roberts' attempt to establish a lordship around Trellech in this region was denied by the courts.
Welsh Marches (accept descriptive answers before last sentence; prompt on England or Wales)