According to the legend Danebrog fell from the sky during Volmerslaget, Volmer battle to defeat the heathens and secure Estonia for Christianity, near Lyndanisse in 1219, which they won.
The first historical mentioning of the Danebrog is from the Dutch herald Gelre´s Book of Arms from 1370, in which the Danish King´s shield is described as a red cloth with a white cross. This Danish King was Valdemar Atterdag.
However, Danebrog is one of the oldest Christian-European flags, of the same generation as the red-white flags of Austria, England and the Maltese knights. France, too, had a red flag with a white cross in those days, as had the Holy Roman-German empire.
Fly proud and high, Danebrog!