Liber Extra
He became blind at the age of forty-four. This affliction did not prevent him from devoting himself to canonical studies and from writing a commentary of the Decretals of Gregory IX, which gained for him the title of "Doctor Caecus Oculatissimus", i.e. the blind yet most far-sighted doctor. This commentary includes interpretations of the texts of the most difficult of the Decretals of Gregory IX. It is distinguished by the clearness with which the most complex and disputed questions of canon law are explained. The work is also of value for the purpose of ascertaining the practice of the Roman Congregations, especially that of the Congregation of the Council, of which the author quotes numerous decisions.