By 1455 he had arrived at Paris and entered upon his studies for the theological degree. Within a year he conceived a profound distaste for the philosophy dominant in the schools; and though he persevered for some time, his frequent dissension from his teachers earned for him the title of 'Magister contradictionis'. After this his movements cannot be traced until 1470, when he was at Rome in the train of Cardinal Francesco della Rovere. In the interval he studied medicine, and, if report be true, travelled far; venturing into the East, just when the fall of Constantinople had turned the tide of Hellenism westward. In Greece he read Aristotle in the original, and learnt to prefer Plato; in Egypt he sought in vain for the books of Solomon and a mythical library of Hebrew treasures.
In 1471 his Cardinal-patron was elected Pope as Sixtus IV. The magnificence which characterized the poor peasant's son in his dealings with Italy, in his embellishment of Rome and the Vatican, was not lacking in his treatment of Wessel. 'Ask what you please as a parting gift', he said to the scholar, who was preparing to set out for Friesland. 'Give me books from your library, Greek and Hebrew', was the request. 'What? No benefice, no grant of office or fees? Why not?' 'Because I don't want them', came the quiet reply. The books were forthcoming--one, a Greek Gospels, was perhaps the parent of a copy which reached Erasmus for the second edition of his New Testament.
After his return to the North, Wessel was invited to Heidelberg, to aid the Elector Palatine, Philip, in restoring the University, _c._ 1477. He was without the degree in theology which would have enabled him to teach in that faculty, and was not even in orders: indeed a proposal that he should qualify by entering the lowest grade and receiving the tonsure, he contemptuously rejected. So the Theological Faculty would not hear him, but to the students in Arts he lectured on Greek and Hebrew and philosophy. For some years, too, he was physician to David of Burgundy, Bishop of Utrecht, whom he cured of gout by making him take baths of warm milk. The Bishop rewarded him by shielding him from the attacks of the Dominicans, who were incensed by his bold criticisms of Aquinas; and when age brought the desire for rest, the Bishop set him over a house of nuns at Groningen, and bought him the right to visit Mount St. Agnes whenever he liked, by paying for the board and lodging of this welcome guest.