Abraham bar Hiyya Ha-Nasi

Abraham bar Ḥiyya ha-Nasi (c. 1070 – 1136 or 1145), also known as Abraham Savasorda, Abraham Albargeloni, and Abraham Judaeus, was a Catalan Jewish mathematician, astronomer, and philosopher who resided in Barcelona. He was the great-grandson of Hezekiah ben David, the last Gaon of the Talmudic academies in Babylonia. Bar Ḥiyya held a high position in the royal court, serving as minister of police and bearing the title of governor ('nasi'). He is considered a significant figure in the scientific movement that made Jews in Provence, Spain, and Italy intermediaries between Arabic science and the Christian world. He was active in translating Islamic scientific works into Latin and is credited with introducing algebra into Christian Europe. Bar Ḥiyya authored original works on mathematics, astronomy, Jewish philosophy, chronology, and surveying. His most influential work, *Ḥibbur ha-Meshiḥah ve-ha-Tishboret* (translated into Latin as *Liber embadorum*), published in 1145, contained the first known complete solution of the quadratic equation and significantly impacted Fibonacci's work. He wrote in Hebrew, promoting its use for scientific purposes. His other works include *Yesode ha-Tebunah u-Migdal ha-Emunah* (an encyclopedia of mathematics), *Hegyon ha-Nefesh* (on repentance), and *Megillat ha-Megalleh* (on the redemption of the Jewish people). He also collaborated on translations of scientific works from Arabic into Latin, including Ptolemy's *Tetrabiblos*. Bar Ḥiyya's philosophical system was Neoplatonic, and he distinguished three classes of pious men and three corresponding groups of Torah laws. He was a believer in astrology, calculating a date for the advent of the Messiah.