9th-10th century Huns and Avars may have had skull trephination performed on them for ritual purposes.  The skin was pulled away and a section of the outer surface of the bone was removed, then the skin replaced.  When the wound healed, it would look like a depression.  Sort of like a skull tattoo in relief…?
Via @HenryRothwell on Twitter

9th-10th century Huns and Avars may have had skull trephination performed on them for ritual purposes.  The skin was pulled away and a section of the outer surface of the bone was removed, then the skin replaced.  When the wound healed, it would look like a depression.  Sort of like a skull tattoo in relief…?

Via @HenryRothwell on Twitter

(Source: bonesdontlie.wordpress.com)