The effect of Offa's Dyke ... No longer could the Welsh kingdoms consider themselves as part of an interrelated set of peoples occupying almost the whole of the British landmass. The realisation of this probably fostered the development of the name Cymry, 'comrades', which came to be the Welsh people's own name for themselves. However great their internal arguments and dissensions, they were aware of an essential unity. To the Anglo-Saxons, they were the Wallas, 'foreigners' a name which leads directly to present-day Welsh.
David Ross, Wales: History of a Nation
Offa’s dyke was constructed in the 790′s by King Offa of Merica. It was a giant earthwork that created a visual border to separate Wales and what would eventually become England. In many places Offa’s dyke can still be seen today.
