In 1536 Vesalius returned to Brabant to spend another year at the Catholic University of Leuven, where the influence of Arab medicine was still dominant. Following the prevailing custom, he prepared, in 1537, a paraphrase of the work of the 10th-century Arab physician, Rhazes, probably in fulfillment of the requirements for the bachelor of medicine degree. He then went to the University of Padua, a progressive university with a strong tradition of anatomical dissection. On receiving a doctoral degree in medicine the same year, he was appointed a lecturer in surgery with the responsibility of giving anatomical demonstrations. Since he knew that a thorough knowledge of human anatomy was essential to surgery, he devoted much of his time to dissections of cadavers and insisted on doing them himself, instead of relying on untrained assistants. At first, Vesalius had no reason to question the theories of Galen, the Greek physician who had served the emperor Marcus Aurelius in Rome and whose books on anatomy were still considered as authoritative in medical education in Vesalius’s time. In January 1540, breaking with this tradition of relying on Galen, Vesalius openly demonstrated his own method—doing dissections himself, learning anatomy from cadavers, and critically evaluating ancient texts. He did so while visiting the University of Bologna. Such methods soon convinced him that Galenic anatomy had not been based on the dissection of the human body, which had been strictly forbidden by the Roman religion. Galenic anatomy, he maintained, was an application to the human form of conclusions drawn from the dissections of animals, mostly dogs, monkeys, or pigs. It was this conclusion that he had the audacity to declare in his teaching as he hurriedly prepared his complete textbook of human anatomy for publication. Early in 1542 he traveled to Venice to supervise the preparation of drawings to illustrate his text, probably in the studio of the great Renaissance artist Titian. The drawings of his dissections were engraved on wood blocks, which he took, together with his manuscript, to Basel, Switzerland, where his major work De humani corporis
 fabrica libri septem (“The Seven Books on the Structure of the Human Body”) commonly known as the Fabrica, was printed in 1543