<p style='text-align: justify;'>On the first folio of the Bible now known as Durham Cathedral Library MS A.II.4, Symeon of Durham provides a list of 49 books bequeathed to the Cathedral by its sometime Bishop, William of Saint-Calais (Bishop of Durham, 1080-1096). Among the works of Bede and the Church Fathers, the breviaries, missals, and homiliaries, is a volume noted only as Decreta Pontificum. This book, now Peterhouse MS 74, is one of the college’s most important manuscripts, an annotated copy of the pseudo-Isidorean decretals known to modern historians as the <i>Collectio Lanfranci</i>. In short, it is a book of early English canon law, the text of which was originally brought over from Normandy with Lanfranc of Bec (Archbishop of Canterbury, 1070-89). The Peterhouse copy is one of two early versions of the material (the other being Cambridge, Corpus Christi College MS 130) probably derived – if not actually copied – from Lanfranc’s own book, now Trinity College, Cambridge MS B.16.44. </p><p style='text-align: justify;'>The manuscript is perhaps most well-known for having once been part of a legal dispute between Bishop William and his detractors, who, during a political fracas in 1088, accused him of conspiracy against the King, William Rufus. The Bishop was called to the court at Old Sarum, where he repeatedly made reference to his book of canon law to maintain his rights and position, namely that a bishop could not be tried in a secular court, but should answer only to Rome. Ironically, Lanfranc himself was Bishop William’s adversary in the case, and he argued that the bishop was being tried not as a clergyman, but as a landholder and potential traitor to the throne. Following the trial, William of Saint-Calais was stripped of his title and returned to Normandy until 1091, when he regained favour with the King and was reestablished at his see at Durham. The legal mêlée must have prompted some public interest, as a contemporaneous work detailing the proceedings was composed, <i>De Iniusta Vexacione Willelmi Episcopi Primi</i>, and survives in 6 manuscripts (Bodleian MS Fairfax 6, Bodleian MS Laud misc 700, Lincoln's Inn Library Hales MS 114, British Library Cotton MS Claudius D IV, British Library Harleian MS 4843, and Durham Bishop Cosin’s Library MS V ii). The text makes reference to William’s book of canon law, our very own Peterhouse MS 74. </p><p style='text-align: justify;'>The book remained in Durham until at least 1604, and arrived in Peterhouse no longer than a century later.</p><p style='text-align: justify;'>This manuscript is notable for surviving in a 12<sup>th</sup> century binding.</p>