Combination of symbols represented on a piece of cloth, serving as a medium of social, typically political, communication. It is usually rectangular and attached by one edge to a staff or is hoisted on a pole with halyards. Flags appear to be as old as civilized human society, though their origin is not well understood. The Chinese may have been the first to develop cloth flags, and it is believed that they were introduced to Europe by returning Crusaders. Most national flags in use today were designed in the 19th and 20th centuries.