Popular in the Middle Ages as a prayerbook as well as essential to church services, the psalter also presented an important text for Christian theologians. They wrote many commentaries on the psalms, to explain them in Christian terms and connect them with church doctrine. Peter Lombard (circa 1100-1164), theologian and leading light at the cathedral school of Notre Dame in Paris, compiled and organized excerpts from earlier interpretations. His aim was not to create something original but to make a book that would be useful for theologians to study. This was also his goal in his most famous accomplishment, 'Sentences', which unified the whole of doctrine into a textbook. This manuscript's pages have a specialized study lay-out with the psalm in a central column and on either side the pertinent sections of his commentary. No one knows for sure where in England this manuscript was made, although it dates from during or soon after his lifetime, and it was in the library at St Augustine's, Canterbury, by the end of the 15th century. Peter had connections with English theologians, such as Stephen Langton, Archbishop of Canterbury (1208-1228), who owned the original copy of the 'Sentences.' Psalm 41 (42) and its commentary show the page layout. The psalm begins with a large decorated letter and is written in large script. Peter's 'Commentary' to either side is in small script, with psalm verses abbreviated and underscored in red. In the margins abbreviated notes of sources are written in red: Cassiodorus, Jerome, and others. The lines setting out the complicated arrangement are clearly visible.