I was thinking of the 600s to 800s (or so), before Norsemen really came on the scene. Even with some cross-polination from Irish, Saxons, and possibly French, it was largely speaking its own unique language (discounting Cornish and Cumbric). My point is that the lasting influence of that language is what kept the idea of Wales intact even when it was no longer an independent country.
To quote the banner of the paper in my hand (Y Cymro): Cenedl heb iaith, cenedl heb galon - A nation without a language is a nation without a heart