Mounted Norman knights attack from both sides. The shield-wall is a tightly packed formation of overlapping shields, with a dense array of spears protruding in front to receive the cavalry charge. The shield wall proved to be an effective defence for the English as the Norman cavalry had a difficult time trying to break the shield wall. It was quite late in the day when the wall was finally broken. The difficulty was that in order to use the sword in this situation it was necessary to turn the horse side on to the wall. This left the horse vulnerable to attack, as horse armour was not in use at this time. The term 'right hand man' is said to derive from the shield wall formation.