Letter 10
First Leo states that the unity of the Church is based upon its subordination to the see of Rome whose authority comes from the primacy given to Peter the Apostle by Christ. Then, Leo refers to the case of Bishop Hilary of Arles who usurps for himself the primacy in the province of Vienne, and thereby denies his subordination to Rome. Then, he speaks about the case of Bishop Celidonius of Besançon who was deposed by Hilary but appealed to the Pope and obtained the lifting of this sentence.
3. [...] Celidonius, the bishop, was therefore acquitted, for he had proved himself wrongfully deposed from the priesthood, by the clear replies of his witnesses made in his own presence: so that Hilary, who remained with us, had no opposition to offer. The judgment, therefore, was rescinded, which was brought forward and read to the effect that, as the husband of a widow, he could not hold the priesthood. Now this rule we, maintaining the legal constitutions, have wished scrupulously adhered to, not only in respect of priests but also of clergy of the lower ranks: that those who have contracted such a marriage, or those who are proved not to be the husbands of only one wife contrary to the apostle's discipline, should not be suffered to enter the sacred service. But though we decree that those, whom their own acts condemn, must either not be admitted at all, or, if they have, must be removed, so those who are falsely so accused we are bound to clear after examination held, and not allow to lose their office. [...]
Further on, Leo deals with a case of deposition of Bishop Projectus by Hilary and also restores Projectus to his see (par. 4-5). Then he condemns the practice of Hilary of using the military force to intervene in the episcopal elections in Gaul. He repeats what rules should be observed during those elections (the approval of the people and the clergy is needed, the metropolitans should not overstep their jurisdiction, the ordination should by celebrated on Sunday; par. 6). Hilary is devested not only from his usurped jurisdiction but also from the metropolitan jurisdiction over the province of Vienne (par. 7). Leo forbids bishops (sacerdotes) to excommunicate laymen for trivial things (par. 8). Bishop Leontius is appointed in place of Hilary as the metropolitan bishop.
(trans. Ch. Lett Feltoe 1895: 8-13; summary M. Szada)