Bonizo of Sutri or Bonitho was a Bishop of Sutri and then of Piacenza in central Italy, in the last quarter of the 11th century. He was an adherent of Gregory VII and an advocate of the reforming principles of that pope. He wrote three works of polemical history, including Liber ad amicum, which detailed the struggles between civil and religious authorities. He was driven out of both of his dioceses, once by the emperor and once by opponents of Gregorian-style reform. Source: Wikipedia (en)