Where does “brogos” come from?

brogos (Proto-Brythonic) comes from Proto-Celtic mrogis, from Proto-Indo-European morǵ- — edge, boundary, border; frontier, border.

brogos (Proto-Brythonic): country

Definitions

Step	Language	Word	Meaning
1	Proto-Celtic	mrogis	border, borderland, march, mark; region, country,...
2	Proto-Indo-European	morǵ-	edge, boundary, border; frontier, border

brogos — Etymology, Origin & Word History | Etymology Explorer