War flag

The word standard itself is from an Old Frankish term for a field sign (not necessarily a flag).

The use of flags as field signs apparently emerges in Asia, during the Iron Age, possibly in either China or India.

The Roman Vexillum itself is also "flag-like" in the sense that it was suspended from a horizontal crossbar as opposed to a simple flagpole.

Use of simple flags as military ensigns becomes common during the medieval period, developing in parallel with heraldry as a complement to the heraldic device shown on shields.

Thus, the city of Lucerne used a blue-white flag as a field sign from the mid 13th century, without deriving it from a heraldic shield design.