Hillel II (Hebrew: הלל נשיאה, Hillel the Nasi), also known simply as Hillel, was an amora of the fifth generation in the Land of Israel. He held the office of Nasi of the Sanhedrin between 320 and 385 CE. He was the son and successor of Judah III. He is sometimes confused with Hillel the Elder, as the Talmud sometimes simply uses the name "Hillel". Biography In two instances his name is quoted in connection with important decisions in Jewish law: in one, Jose ben Abin expounds to him a law; in the other, Hillel cites a mishnah to establish a law. The emperor Julian the Apostate was gracious to Hillel, whom he honored on a number of occasions. In an autograph letter to him, Julian assured him of his friendship and promised to ameliorate further the condition of the Jews. Before setting out for the war with Persia, Julian addressed to the Jewish congregations a circular letter in which he informed them that he had "committed the Jewish tax-rolls to the flames," and that, "desiring to show them still greater favors, he has advised his brother, the venerable patriarch "Julos", to abolish what was called the 'send-tax'". Fixing of the calendar He is traditionally regarded as the creator of the modern fixed Jewish calendar. This tradition first appears in a responsum of R. Hai Gaon (written in 992) cited by R. Abraham bar Hiyya in his Sefer Ha'ibbur (written in 1123). The citation explicitly refers to the year that this event happened, 670 of the Seleucid era, which corresponds to 358/9 CE. However, a number of documents have been found that indicate the calendar was not fully fixed in Hillel's time; most famously a letter found in Cairo Geniza (from the year 835/6) indicates that the holidays were observed on different dates from those predicted by the current calendar. The calendar did not reach its exact modern form until at least the years 922-924. According to modern scholar Sacha Stern, Hai Gaon only attributed the establishment of a 19-year cycle, and not other details of the calendar, to Hillel. The fixed calendar was of great benefit to Jews of his and subsequent generations. The Jewish calendar is lunisolar. That is, its months are synchronized with the phases of the moon, but its average year length approximates the mean length of a solar year. The Sanhedrin declared new months based