The Danish flag “Dannebrog” is the oldest flag in the World. It came out of the sky in the year 1219 at June 15, during King Valdemar´s fight in Estonia. Valdemar was King in Denmark from 1202-1248. June 15 is called “Valdemar Day”, it is one of the official Danish flag-days.
Wikipedia : The red banner with a white cross (Danish:Dannebrog) has been the national flag of the Danes since 1219. It is Europe’s oldest flag design still in modern use.