A. Macgeorge, Flags, Glasgow, 1881:

"The vexillium was a standard composed of a square piece of cloth fastened to a cross bar at the top of a spear, sometimes with a fringe all round, and sometimes fringed only below, or without a fringe, but draped at the sides, When placed over the general's tent it was a sign for marching, or for battle. The labarum of the emperors was similar in form, and frequently bore upon it a representation of the emperor, sometimes by himself and sometimes accompanied by the heads of members of his family. [...] That which Emperor Constantine bore was what, in his time, was the only recognized Christian emblem - the first two letters of our Lord's name - the Greek X and P. The labarum was made of silk. The term is sometimes used for other standards, and its form may be recogized in the banners carried in ecclesiastical processions. The labarum, like the vexillium, had sometimes fringes with tassels or ribbons."