Originally published in 1931, this book argues that the twelfth-century political theorist and heretic Arnold of Brescia worked primarily as a religious reformer and only secondarily as a revolutionary in the Commune of Rome. George Greenaway examines the posthumous influence of Arnold’s ideas on the medieval church and on later religious developments, including the Protestant Reformation. This book will be of value to anyone with an interest in medieval heresy, the political history of the papacy and Rome or in the life of Arnold.