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.' The commentary of Peter Lombard begins with an introduction before going on to address each psalm. The first letter is historiated (bears a picture) showing a seated master, who holds an open scroll, with a student, indicating the teaching purpose of the commentary. Most of the inscriptions written in red in the margins are 'footnotes' referencing sources in Augustine, John the Scot, Cassiodorus, and others.