Question: Cynfarch Oer, was probably a 6th-century king of the Sub-Roman realm of Rheged, was one of the kingdoms of the "Hen Ogledd" ("Old North"), the Brittonic-speaking region of what is now Northern England, and southern Scotland, during the post-Roman era, and which time period?
Sentence (from "Kingdom of Strathclyde"): It is also known as Alt Clut, a Brittonic term for Dumbarton Castle, the medieval capital of the region.
Relevant evidence: No