In the seventh and eighth century mounted troops in what is now France used their spear under arm and pointed their horse at the enemy, rather than hitting out to the side in the older fashion. This style meant they could balance a longer spear, that spear became the lance. With this new style of fighting a tight fitting shield was needed, one that covered the whole leg as you charged headlong. The kit shield was developed with its taper that meant it could be held close to the body, covering nearly all the left side. Viking Invaders of Northern France liked this shield. When warriors were massed in tight shield walls the taper blocked under cuts to their legs. The Anglo-Saxons copied the Vikings and used this shield for their heavy armed House Carl infantry. Our Norman ancestors were descended from Viking invaders of France, so we tend to think of this as a Viking or Norman shield.