[...The Romans found a disunified group of tribal kingdoms organized around the same logic of warfare as the Gauls. Most of the tribes were new arrivals—the bulk of southern Britain had been conquered by the Belgae from northern Gaul. In the process of emigrating to the island, the Celts pushed the native populations north—these refugee tribal groups would become the cultural ancestors of the Picts, a mysterious culture that dominated Scotland until the Irish invasions....]
The above text is taken from the following website:http://www.wsu.edu:8080/~dee/MA/CELTS.HTM
(text can be found under the head 'Britain' in the text, thus scroll down)
The nowadays Welshmen are from Celtic origin as well. They came from Northern Gaul.
Also, Arthen was once a king of Ceregidion and there are more men in the history of Wales that are called Arthen.
See for the following websites:http://freepages.genealogy.rootsweb.com/~syroots/html/d0005/g0000082.htmlhttp://www.geocities.com/bpstratton/gedcom/d0001/g0000064.html#I2420