Military colours, standards and guidons

In military organizations, the practice of carrying colours, standards, flags, or guidons, both to act as a rallying point for troops and to mark the location of the commander, is thought to have originated in Ancient Egypt some 5,000 years ago. The armies of the Roman Empire also used vexilla, battle standards reading SPQR. It was formalized in the armies of Europe in the High Middle Ages, with standards being emblazoned with the commander's coat of arms.

Source: Wikipedia — Military colours, standards and guidons (CC BY-SA 4.0)