Saint Gregory I
The two chief features of Gregory's lasting work are the enforcement of the papal supremacy and the establishment of the temporal position of the pope. Gregory not only legislated minutely and carefully for his immediate charges, but he interfered when necessary outside Italy; e.g., he attacked Donatism in Africa and simony in Gaul. Most significantly, he refused to recognize ecumenical as a title of the patriarch of Constantinople, since that title was not consistent with the divine vicegerency of the pope.
The exarch of Ravenna, representative of the Byzantine emperor in the West, claimed secular jurisdiction over Rome, and Gregory acknowledged it de jure. However, the exarch, Romanus, did nothing to help the city when it was threatened by a Lombard attack in 592. Gregory, as bishop of Rome, took command and negotiated a peace. It was ignored by the exarch, and the Lombards resumed their attack on Rome. Since Romanus deferred making peace, Gregory began independent negotiations, a new affront to the imperial dignity and an extralegal act.
In his dealings with the Lombards and the exarch, Gregory showed that if the emperor would not defend the pope, the pope would defend himself and by doing so would make himself temporally independent. Thus he set a precedent that enabled the papacy to prevent the total destruction of Rome. Yet Gregory was the important exponent of the doctrine of divided powers: the emperor was God's vicar in things temporal, the pope in things spiritual.
Gregory's encouragement of monasticism was significant historically, and his insistence on clerical celibacy and the exemption of the clergy from trial in civil courts bore great fruit later. St. Gregory contributed to the development of the Gregorian chant or plainsong. He was succeeded by Sabinian.