The Battle of Ballon took place on 22 November 845 between the forces of Charles the Bald, king of West Francia, and Nominoë Duke of Brittany. Nominoë was appropriating border territory and opposing Charles' attempt to impose Frankish authority. Nominoë defeated Charles, initiating a period of Breton expansion and consolidation of power.
Following his defeat, rumors circulated that Charles had been killed, forcing him to make a quick public appearance in Maine. While there he rebuilt his army, and headed back towards Brittany late in 846. There he concluded a treaty with Nominoë, though the exact content of the agreement is unknown. Despite this a "cold war" persisted, and Breton raids continued into Frankish territory at Christmas of that year. Nevertheless the agreement remained unbroken until 849.
This relatively minor battle is often confused with the much more decisive Battle of Jengland won by Nominoë's son Erispoe against Charles in 851. This confusion dates to Arthur de la Borderie's 1894 History of Brittany and has been repeated many times since. However, it is to the battle of Ballon that some date the birth of a unified and independent Brittany, behind a single sovereign: Nominoë. The expansionist policy of Nominoë, by the conquest of the former Marches of Brittany, a Frankish buffer zone, was continued by Erispoe, who consolidated the borders of medieval Brittany.
In the twentieth century the battle was given emblematic status by Breton nationalists. In 1952 the battle was commemorated by the nationalist group Koun Breizh, who funded the erection of a statue of Nominoë by the artist Raffig Tullou in Bains-sur-Oust, near the site of the victory. Another nationalist group, Bretagne 845, founded in 1982, was named from the date of the battle. It merged with Koun Breizh in 1994