On this subject, I'm currently going through the third edition of Montross's War Through The Ages, and she cites a quote from Procopius that is related, regarding the horse-archers of the Byzantine Empire of AD 530.

But the bowmen of the present time go into battle wearing corselets and fitted out with greaves which extend up to the knee. From the right side hang their arrows, from the other the sword. And there are some who have a spear also attached to them and, at the shoulders, a sort of small shield without a grip, such as to cover the region of the face and neck. They are expert horsemen, and are able without difficulty to direct their bows to either side while riding at full speed, and to shoot an opponent whether in pursuit or in flight. They draw the bowstring along by the forehead about opposite the right ear, thereby charging the arrow with such an impetus as to kill whoever stands in the way, shield and corselet alike having no power to check its force.
Does anybody have sources to dispute this, or more details on the "corselet" of the era?