But if a ruler of high mental gifts is always destined to exert a powerful influence upon his epoch, how much more telling is this influence when the contemporaries of such a monarch lead a mental life, fettered by so many religious, philosophical, and physical prejudices as undeniably dominated mankind during the reign of the great Hohenstaufen. If these conditions were of the greatest advantage to astrology in general, circumstances shaped themselves most favorably for _Medicina Astrologica_ in particular. Very soon after the death of the star-learned Hohenstaufen emperor, two highly talented physicians bound themselves body and soul to astrology—namely, Arnald Bachuone, called also, after his birthplace, Villanueva, Arnaldus Villanovanus or Arnald of Villanova (1235-1312), and Petrus, called also, after his birthplace, Abano near Padua, Petrus de Apono or Petrus Aponensis (1250-1315). From that time until the seventeenth century the most eminent representatives of all the sciences and professions devoted themselves to the doctrines of astrology. In the excellent work of Sudhoff is cited a notable number of physicians—by no means the most unskilful of their day—who confessed themselves to be iatromathematicians (_i.e._, _medici astrologici_). Astrology, and with it _Medicina Astrologica_, reigned supreme at most of the princely courts from the thirteenth to the seventeenth centuries. The Hohenstaufen, Frederick II., was, as we have seen, an implicit adherent to astrologic doctrines; likewise the Visconti in Milan. The royal court of Aragon in Palermo offered a sheltering asylum to astronomy and to astrology. Alfonso X. of Castile was so enthusiastic a friend of scientific astronomy that he ordered the planet-tables of Ptolemy to be restored, with an outlay of enormous costs, by fifty astronomers called by him to Toledo. German princes, such as Elector Joachim of Brandenburg, Albrecht, Elector of Mayence, Landgrave William of Hesse, Duke Albrecht of Prussia, not only adhered to the predictions of the stars, but they also subscribed to the statements of astrological medicine. Thus, for instance, Thomas Erastus (died 1583) the well-known opponent of Paracelsus, tells us that, as body-physician to the reigning count of Henneberg, he was not permitted to begin a course of treatment until he had consulted the stars. The German emperor, Charles V., was quite as constant a friend of the astrologists; he was instructed in astrology by his teacher, the subsequent pope, Hadrian VI. The court of Denmark was the center of astrological teachings under Frederick II., as no less a personage than Tycho de Brahe was active there. But not only rulers favored astrology, it met with implicit belief from highly enlightened scholars, statesmen, and naturalists. Thus, Melanchthon was so convinced an adherent of all astrological doctrines that he was incessantly active in their favor by mouth and by pen. And when fatal disease had finally seized upon him,