Louis fought him, and gave Aquitaine to Charles the Bald.

The alliance between the three sons of Hermengarde was at once renewed; they raised an army; the emperor marched against them with his; and the two hosts met between Colmar and Bale, in a place called le Champ rouge (the field of red).

Negotiations were set on foot; and Louis was called upon to leave his wife Judith and his son Charles, and put himself under the guardianship of his elder sons.

He refused; but, just when the conflict was about to commence, desertion took place in Louis's army; most of the prelates, laics, and men-at-arms who had accompanied him passed over to the camp of Lothaire; and the field of red became the field of falsehood (_le Champ du mensonge_).
Louis, left almost alone, ordered his attendants to withdraw, "being unwilling," he said, "that any one of them should lose life or limb on his account," and surrendered to his sons.

They received him with great demonstrations of respect, but without relinquishing the prosecution of their enterprise.