Sometime around 1450, mathematician Georg Purbach (1423–1461) began a series of lectures on astronomy at the University of Vienna. Regiomontanus (1436–1476), who was then one of his students, collected his notes on the lecture and later published them as "Theoricae novae planetarum" in the 1470s. This "New "Theorica"" replaced the older "theorica" as the textbook of advanced astronomy. Purbach also began to prepare a summary and commentary on the "Almagest". He died after completing only six books, however, and Regiomontanus continued the task, consulting a Greek manuscript brought from Constantinople by Cardinal Bessarion. When it was published in 1496, the "Epitome of the Almagest" made the highest levels of Ptolemaic astronomy widely accessible to many European astronomers for the first time.