The Kroaz Du (Black Cross, French: Croix Noire) is a flag of Brittany, used as an emblem of the independent duchy in the late Middle Ages.
However, very few Breton barons joined that Third Crusade, so it is more probable that the earliest Kroaz Du was given to Peter I, Duke of Brittany by Pope Gregory IX in 1236 or 1237.
The black cross standard became widely used as the emblem of the Breton soldiers and as the flag for the ships from the end of the Hundred Years' War in the 15th century.
After annexation of 1532, there was never any treaty of union,[1] the admiralty of Brittany kept using the black cross flag for Breton ships (with a modified design).
The Kroaz du has been revived since the late 1990s and was briefly regarded as an emblem of right-wing Breton nationalists (like Adsav), but it is now more and more popular.