This book provides a groundbreaking reinterpretation of the life and career of the preeminent polemicist of the Bishop Bonizo of Sutri. Through a meticulous analysis of Bonizo's literary works and contemporary reports about his activities, the author uncovers the populist roots of both the bishop's reform ideology and his vision of holy war against a heretical emperor, Henry IV of Germany. In establishing the predominance of Bonizo's personal experience as a member of the populist Lombard reform community, the Pataria, in the formation of his thought, this study shatters the picture of a uniform Gregorian party and greatly strengthens the impression of the papal reform movement as a fragile coalition of multiple regional partners, like the Pataria, which enjoyed a fundamental unity of purpose but whose individual constituencies often diverged in their particular strategic objectives. This investigation, moreover, sets Bonizo's story within the context of the urban life of his native Lombardy and examines the relationship between popular religious reform and the gradual development of communal government in northern Italy.