590 AD
Pope St. Gregory I (the Great), elected in 590, transformed the papacy from a primarily spiritual office to an active temporal power. Facing the collapse of Byzantine authority in Italy, he organized the defense of Rome against the Lombards, managed the papal estates, and established the papacy as the guardian of Italian civilization. His 'Moralizations on Job' and 'Pastoral Rule' became standard theological texts for centuries.
Gregory sent Augustine of Canterbury to evangelize England in 597, beginning the Christianization of the Anglo-Saxons. He also reformed liturgical music, creating what would become known as Gregorian Chant. His 'Dialogues' recorded the lives of Italian saints and popularized the concept of Purgatory. Key writings: Moralia in Job, Pastoral Rule, Dialogues, Dialogues on the Life of St. Benedict