The war was fought to decide the territorial inheritances of Charlemagne's grandsons—the division of the Carolingian Empire among the three surviving sons of Louis the Pious.

The battle has been described as a major defeat for the allied forces of Lothair I of Italy and Pepin II of Aquitaine, and a victory for Charles the Bald and Louis the German.

On 24 July 840 in Strasbourg, Lothair precipitated a new civil war by declaring his imperium over all the lands of the empire and, joining with his nephew Pepin, attacked the Loire Valley.

Ermenaud III of Auxerre, Arnoul of Sens, and Audri of Autun pledged themselves for Lothair, while Guerin of Provence and Aubert of Avallon remained with Charles.

According to Andreas Agnellus of Ravenna a total of 40,000[4] men died, including Gerard of Auvergne and Ricwin of Nantes, who fell at Charles' side.

[6] The verses in English are... Fontenoy they call its fountain, manor to the peasant known, There the slaughter, there the ruin, of the blood of Frankish race; Plains and forest shiver, shudder; horror wakes the silent marsh.

Neither dew nor shower nor rainfall yields its freshness to that field, Where they fell, the strong men fighting, shrewdest in the battle's skill, Father, mother, sister, brother, friends, the dead with tears have wept.