He is the last of the three popes listed in the Annuario Pontificio with the title "the Great",[1] alongside Leo I and Gregory I. Nicholas is remembered as a consolidator of papal authority, exerting decisive influence on the historical development of the papacy and its position among the Christian nations of Western Europe.

During his reign, relations with the Byzantine Empire soured because of his support for Patriarch Ignatios of Constantinople, who had been removed from his post in favor of Photius I.

[5] To a spiritually exhausted and politically uncertain Western Europe beset by Muslim and Norse incursions, Pope Nicholas appeared as a conscientious representative of Roman primacy in the Church.

[7] Archbishop John of Ravenna oppressed the inhabitants of the Papal States, treated his suffragan bishops with violence, made unjust demands upon them for money, and illegally imprisoned priests.

Having first visited the Emperor Louis at Pavia, the archbishop repaired with two imperial delegates to Rome, where Nicholas cited him before the Roman synod assembled in the autumn of 860.

Hincmar opposed the appeal to the pope, but eventually had to acknowledge the right of the papacy to take cognizance of important legal causes (causae majores) and pass independent judgment upon them.

At the Council of Metz, June 863, the papal legates, bribed by the king, assented to the Aachen decision, and condemned the absent Teutberga, who took refuge in the court of Lothair's uncle, Charles the Bald, and appealed to the Pope.

The two archbishops, Günther of Cologne and Thietgaud of Trier, both rumoured to be relatives of Waldrada, had come to Rome as delegates, and were summoned before the Lateran Synod of October 863, when the pope condemned and deposed them as well as John of Ravenna and Hagano of Bergamo.

Emperor Louis II took up the cause of the deposed bishops, while King Lothair advanced upon Rome with an army and laid siege to the city.

Subsequently, Engelberga arranged a reconciliation with the pope,[8] the emperor withdrew from Rome and commanded the former archbishops of Trier and Cologne to return to their homes.

Another matrimonial case in which Nicholas interposed was that of Judith, daughter of Charles the Bald, who had married Count Baldwin I of Flanders without her father's consent.

Frankish bishops had excommunicated Judith, and Hincmar of Reims had taken sides against her, but Nicholas urged leniency in order to protect freedom of marriage.

[9] For a variety of reasons, Prince Boris I of Bulgaria became interested in converting to Christianity and undertook to do that at the hands of western clergymen to be supplied by King Louis the German of East Francia in 863.

Unhappy with Byzantine influence and desiring an autocephalous status which Photius was unwilling to grant, Boris sent an embassy to Nicholas with 106 questions on the teaching and discipline of the Church in August 866.

Nicholas answered these inquiries in his "Responsa Nicolai ad consulta Bulgarorum" (Giovanni Domenico Mansi, "Coll.

In 866, the Bulgar Kahn St Boris the Baptiser wrote to Pope Nicholas asking a wide range of questions, one of which being whether or not it was sinful for Christians to wear pants.

Regino of Prüm reports that Nicholas was highly esteemed by the citizens of Rome and by his contemporaries generally (Chronicon, "ad annum 868," in "Mon.

After exhaustive investigation, Heinrich Schrörs concluded that the pope was neither acquainted with the pseudo-Isidorian collection in its entire extent, nor did he make use of its individual parts.

[13] Perhaps the most impactful act of Pope Nicholas was, in the year 866, he ordered that all Christians should abstain from eating the "flesh, blood, or marrow"[14] of warm-blooded animals on Wednesdays and Fridays.