Body piercing is as old as civilization, and was practiced in almost all cultures, including the Vikings (which would of course include the Normans) as well as the Anglo-Saxons. It was a straightforward means of carrying personal wealth on one's person, and quickly came to signify status (like walking around with a wad of $100 bills thumbtacked on one's forehead). In the case of human chattel slaves, a noble, monarch, or other person of means could use enslaved persons to carry their enslaver's wealth for convenience.