Liber ad amicum
Liber ad amicum is a historical work by Bonizo of Sutri written during the Investiture Controversy. Regarded as one of Bonizo's most well-known and influential works, Liber ad amicum chronicles the life of Pope Gregory VII and papal-imperial relations from the time of Constantine the Great to Gregory. It also details the individual histories of the Patarene movement that Bonizo belonged to and the House of Canossa.