“Frederick at this time was chiefly solicitous about Sicily, towards which he was drawn by his Norman parentage on the mother's side, while the character of his own German people did not attract his sympathies. He had grown up in Sicily where Norman, Greek, and Mohammedan civilization had intermingled, at once strengthening and repelling one another. The king, endowed with great natural ability, had acquired a wonderful fund of learning which made him appear a prodigy to his contemporaries, but, although he was intimately acquainted with the greatest productions of eastern and western genius, his soaring spirit never lost itself in romantic dreams. He eagerly studied both the more and the less important interests of the political and economical life of Southern Italy. The funding of the University of Naples sufficiently attests his interest in education. He was an intelligent admirer of the beauties of nature, his love for which was intensified by his natural powers of observation. The unlimited resources of the physical world and its constantly multiplying problems increased the inclination of this sceptical spirit towards a thorough empiricism. In none of his contemporaries does intellectual subjectivism show itself so strongly and at the same time so one-sidedly. This desire to penetrate into the secrets of the universe, as well as his scandalous sensual indulgence, brought on Frederick the reputation of an atheist.”

See main: Soul experiments

“Frederick II, this pestilent king, a scorpion spitting out poison from the stinger of his tail, has notably and openly stated that—in his own words—the whole world has been fooled by three imposters, Jesus Christ, Moses, and Muhammad, two of whom died honorably, while Jesus himself died on the cross. Moreover, he has dared to affirm, or rather, he has fraudulently claimed, that all those who believe that a virgin could give birth to the god who created nature, and all the rest, were fools. And Fredrick has aggravated the heresy by this insane assertion, according to which no one can be born without having been conceived by the prior intercourse of a man and woman; he also claims that people ought to believe nothing that cannot be proven by the strength and reason of nature.”

— Pope Gregory IX (1239), address to monarchs

“Frederick II was man of extraordinary culture, energy, and ability – called by a contemporary chronicler stupor mundi (the wonder of the world), by Nietzsche the first European, and by many historians the first modern ruler – Frederick established in Sicily and southern Italy something very much like a modern, centrally governed kingdom with an efficient bureaucracy.”

— Donald Detwiler (1999), Germany: A Short History [1]

“How much longer can this deception last?”

— Frederick II (c.1235), remarked at sight of priest on his way to administer last rights [2]

“The soul dissipates like a breath and rots like an apple, given that fruit, like man, is made up of four essences.”

— Frederick II (c.1235) [2]