  Scholars agree that On the Trinity is the earliest work in the Magisterium and that it was probably written in the early 1220s. Parts of other works can be partially dated by references to contemporaneous events, though the sheer size of many individual works suggests they were probably written over a period of years. The whole Magisterium itself was probably written during a period extending from the early 1220s to around 1240, with On the Universe written in the 1230s and On the Soul completed by around 1240.