Closest to what we think of as a modern "flag", the medieval banner was more vertical in shape. Typically, the proportions were approximately 2 units horizontally to three vertically. A medieval banner might also include multiple tongues from the fly (the end opposite to the pole) as in the second example above, or a long tongue from the top edge as in the third example above (in which case it's called a "schwenkle").


Seals of the landgrave Conrad II of Thuringia, about 1234. Banner and
gonfanon.
Oldest known representation of the Danebrog (national flag of Denmark),
Banner, late 14th C.








Flags with pavilions, banners and pennants, 14th C.




Les tres riches heures du Duc de Berry. Flags and pennons, 1412-1416.

Elizabethan funeral procession. Banners, 1603.

Crusader from an early 14th C. manuscript.

Crusaders from a 14th C. manuscript.
Knighting of a Young Man by Paris, 1233.