In his inimitable manner Gibbon describes the fierce struggle the Greek Catholic Church had to wage before she obtained a foothold in Russia, but he neglects to mention the fact that Judaism no less than paganism was among her formidable opponents. The contest lasted several centuries, and in many places it is undecided to this day.[15] The Khazars, who had become proselytes in the eighth century, were constantly encroaching upon Russian Christianity. Buoyant as both were with the vigor of youth, missionary zeal was at its height among the two contending religions. Each made war upon the other. We read that Photius of Constantinople sent a message of thanks to Archbishop Anthony of Kertch (858-859) for his efforts to convert the Jews; that the first Bishop of the Established Church (1035) was "Lukas, the little Jew" (Luka Zhidyata), who was appointed to his office by Yaroslav; and that St. Feodosi Pechersky was fond of conversing with learned Jews on matters of theology.[16] On the other hand, the efforts of the Jews were not without success. The baptism of the pious Olga marks an era in Russian Christianity, the beginning of the "Judaizing heresy," which centuries of persecution only strengthened. In 1425, Zacharias of Kiev, who is reputed to have "studied astrology, necromancy, and various other magic arts," converted the priest Dionis, the Archbishop Aleksey, and, through the latter, many more clergymen of Novgorod, Moscow, and Pskov. Aleksey became a devout Jew. He called himself Abraham and his wife Sarah. Yet, strange to say, he retained the favor of the Grand Duke Ivan Vassilyevich, even after the latter's daughter-in-law, Princess Helena, his secretary Theodore Kuritzin, the Archimandrite Sosima, the monk Zacharias, and other persons of note had entered the fold of Judaism through his influence.