Hermengarde, who, with the consent of her mother, lived at the court of her relation, the duke of Friouli, with his and her own secret approbation, was carried off by Boson, brother of Richildis, wife of Charles the Bald, and married to him in 877. Boson, whom his brother-in-law, dead about two years before, had made duke of Provençe, at the instigation of his wife, caused himself to be proclaimed king, in 879; and, by his courage and ability, preserved the crown he had usurped, though attacked by the brother kings of France. In 881, Charles the Fat, being in Italy, caused the empress Angelberga to be taken from the monastery where she resided, and carried prisoner into Germany. It was supposed she might assist Hermengarde and her husband, by her riches and political knowledge, and he meant to serve Lewis and Carloman by her confinement; yet, when he came to Rome to receive the imperial crown, her friend, the pope, demanded the liberty of Angelberga, which Lewis promised, provided the kings of France consented. On which John wrote to them in a very spirited manner: he said this princess was under the protection of the apostolical see, to which the emperor Lewis II. had recommended her; and prayed them to consent that she might be sent back to Rome, where he himself would so well guard her, that she should not even aid, by her counsels, her son-in-law and her daughter.
He also wrote, on this subject, a circular letter to all the archbishops, bishops, and counts of Italy, to engage them to attempt the deliverance of Angelberga; and the next year, by letter, besought the reigning empress to intercede with her husband for that purpose. But, notwithstanding all his efforts, he did not obtain his request, till after the kings of France had taken Vienna, which they besieged near two years, and which Hermengarde
