“Vexilles” is the ancient word for flags, they were used to rally population or to signify a membership.
Aztec, Melanesian or Egyptian chiefs used those long decorated and carved sticks, sometimes decorated with feathers, shelves or precious stones.
Roman Legions rose those standards, from the Latin vexillum.
Vexillology then became  the study of flags.

After the discovery of Chinese silk, light and coloured fabrics were raised on bamboos: the first flags.

State flags are usually rectangular in shape and often in the ratio 2:3.
National flags sizes are defined in a reference book : the SHOM(Service Hydrolique et Océanographique de la Marine, i.e.:  French IHO: International Hydrographic Organisation)