Hincmar used his influence with the emperor on behalf of the banished abbot, and not without success: for he stood in high favour with Louis the Pious, having always been a faithful and loyal adherent.

[4] Archbishop Ebbo had been deposed in 835 at the synod of Thionville (Diedenhofen) for having broken his oath of fidelity to the emperor Louis, whom he had deserted to join the party of Lothair.

In the resulting conflicts, in which his personal interest was in question, he displayed great activity and a wide knowledge of canon law, but was not so scrupulous that he would not resort to disingenuous interpretation of texts.

[4] The question of the divorce of Lothair II, king of Lorraine (r. 855–869), who had repudiated his wife Theutberga to marry his concubine Waldrada, engaged Hincmar's literary activities in another direction.

At the request of a number of great personages in Lorraine he composed in 860 his De divortio Lotharii regis et Theutbergae reginae, in which he vigorously attacked, both from the moral and the legal standpoints, the condemnation pronounced against the queen by the Synod of Aix-la-Chapelle (February 860).

Pope Nicholas I, supported him zealously, and in 865, in spite of the protests of the archbishop of Reims, Arsenius, bishop of Orte and legate of the Holy See, was instructed to restore Rothad to his episcopal see.

[4] Hincmar experienced another check when he endeavoured to prevent Wulfad, one of the deposed clerics ordained by Ebbo, from obtaining the archbishopric of Bourges with the support of Charles the Bald.

Hincmar of Laon refused to recognize the authority of his metropolitan, and entered into an open struggle with his uncle, who exposed his errors in a treatise called Opusculum LV capitulorum, and procured his condemnation and deposition at the Synod of Douzy (871).

[4] Although Hincmar had been very hostile to Charles' expedition into Italy, he figured among his testamentary executors and helped to secure the submission of the nobles to Louis the Stammerer, whom he crowned at Compiègne (December 8, 877).

[4] To Carloman, on his accession in 882, Hincmar addressed his De ordine palatii, partly based on a treatise (now lost) by Adalard, abbot of Corbie (c. 814), in which he set forth his system of government and his opinion of the duties of a sovereign, a subject he had already touched in his De regis persona et regio ministerio, dedicated to Charles the Bald at an unknown date, and in his Instructio ad Ludovicum regem, addressed to Louis the Stammerer on his accession in 877.

Besides the works already mentioned, he was the author of several theological tracts; of the De villa Noviliaco, concerning the claiming of a domain of his church; and he continued from 861 the Annales Bertiniani, of which the first part was written by Prudentius, bishop of Troyes, the best source for the history of Charles the Bald.

In one of his letters Hincmar recommended that a copy of Gregory the Great's work called Pastoral Care should be given together with the Book of Canons into the hands of bishops before the altar at their consecration (Schaff).