The national flag of Belgium (Dutch: Vlag van België, French: Drapeau de la Belgique, German: Flagge Belgiens) contains three equal vertical bands of black (hoist side), yellow, and red.
The colours of the Belgium flag were taken from the colours of the Duchy of Brabant, and the vertical design may be based on the flag of France.
The national flag has the unusual proportions of 13:15, but is rarely seen. A flag in a 2:3 or similar ratio is used in most cases, even by most government bodies. The unusual proportions of 13:15 are of unknown origin. – Wikipedia