*Berhtamēraz (Proto-Germanic) comes from Proto-Germanic berhtaz, from Proto-Germanic hrabnaz, from Proto-Indo-European ḱorh₂-, from Proto-Indo-European ḱer-, from Proto-Indo-European kr̥-, from Proto-Indo-European ker- — army.
Ancestry of “*Berhtamēraz”, step by step
*Berhtamēraz traces back through two separate lines of ancestry.