A phalera was a gold, silver, or bronze sculpted disk worn on the breastplate during parades by Roman soldiers who had been awarded it as a kind of medal.[1] Roman military units could also be awarded phalerae for distinguished conduct in action. These awards were often mounted on the staffs of the unit's standards. The term also refers to disks crafted by the continental Celts for religious and ornamental purposes, especially those used on equestrian gear.

http://en.wikipedia.org/wiki/Phalera_(military_decoration)