The Gelre Armorial (Dutch: Wapenboek Gelre) is a Dutch armorial, written between 1370 and 1414. Most historians claim that the book was written by the herald Claes Heinenszoon. The book displays some 1,700 coats-of-arms from all over Europe, in colour. It is now located at the Royal Library of Belgium.

The book is especially important as a historical source, for instance for the history of Denmark. The armorial gives the first known undisputed colour rendering of the Dannebrog – Denmark’s flag, whose precise origin is shrouded in mystery and myth.

On page 55 verso we find the Danish coat-of-arms surmounted by a helmet with horns. Behind the sinister horn is a lance tip with a banner, displaying a white cross on red (see image). The text left of the coat of arms says “die coninc van denmarke” (The King of Denmark). This is the earliest known undisputed colour rendering of the Dannebrog.