An ancient Roman standard consisting of an often decorated (usually) red or purple cloth hung from a cross bar. It is considered to be the first true flag in Western culture, and from which the term vexillology is derived (see also ‘ vexillarius', ‘ vexillifer', ' vexillation' and ‘ vexillology'). Vexillum of the 13th Legion (Eugene Ipavec) Please note however, that whilst frequently described as a cavalry standard (which it was), the vexillum also had a number of other military uses.
The vexillum was a flag-like object used in the Classical Era of the Roman Empire. The vexillum resembles the modern flag; however, the cloth is draped vertically from a horizontal edge, unlike the horizontally-flown flags most used today. The word vexillology, meaning the study of flags, is derived from this word.