-The Vexillum standard is most similar to modern military standards, in that it is a flag. Its bearer was called a vexillarius. -The vexillum was usually white with gold fringe, and letters denoting the legion, cohort and century- like with letters LEG, and COH and a number. -The flag would be red for superior officers, and the chief consul or the emperor's vexillum would be purple, often with the figure of Victory atop it (see right). -Sometimes the flag would also have an icon of an animal, deity, or emperor on it. -The vexillum would be used as the standard for auxiliaries- (allied or subject people, or mercenaries) in the army, cavalry, or a group of infantry detached from the main body of the army for a special purpose. -A red vexillum over a commander's tent meant to prepare for battle!
The flag / labarum of Constantine had the chi-rho symbol on top to symbolize Christianity.