The vexillum was a flag-like object used as a military standard by units in the Roman army. A common vexillum displayed imagery of the Roman aquila on a reddish backdrop.

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 Roman Empire also made battle standards reading SPQR a part of their vast armies. It was formalized in the armies of Europe in the High Middle Ages, with standards being emblazoned with the commander's coat of arms.