Shield bosses, umbos
A shield boss, or umbo, is a round, convex or conical piece of material at the centre of a shield. Shield bosses (or sometimes, just "bosses") are usually made of thick metal but could also be made of wood. The boss was originally designed to deflect blows from the centre of round shields, though they also provided a place to mount the shield's grip. As time went on and heater shields with curved bodies became more popular, and enarmes superseded the bar grip, the boss became more of an ornamental piece.