the Jews, the magnificent development which Arabian culture underwent in his time must have benefited the Jews also; so that a scientific tendency began to make itself noticeable among the Babylonian Jews under Harun and his successors, especially under Al-Ma'mun (813–833). Like the Arabs, the Jews were zealous promoters of knowledge, and by translating Greek and Latin authors, mainly at the House of Wisdom in Baghdad, contributed essentially to their preservation. They took up religio-philosophical studies (the "kalam"), siding generally with the Mutazilites and maintaining the freedom of the human will ("chadr"). The government meanwhile accomplished all it could toward the complete humiliation of the Jews. All non-believers—Magi, Jews, and Christians—were compelled by Al-Mutawakkil to wear a badge; their places of worship were confiscated and turned into mosques; they were excluded from public offices, and compelled to pay to the caliph a tax of one-tenth of the value of their houses. The caliph Al-Mu'tadhel (892–902) ranked the Jews as "state servants." In the 7th century, the new Muslim rulers institute the kharaj land tax, which led to mass migration of Babylonian Jews from the countryside to cities like Baghdad. This in turn led to greater wealth and international influence, as well as a more cosmopolitan outlook from Jewish thinkers such as Saadiah Gaon, who now deeply engaged with Western philosophy for the first time. When the Abbasid Caliphate and the city of Baghdad declined in the 10th century, many Babylonian Jews migrated to the Mediterranean region, contributing to the spread of Babylonian Jewish customs throughout the Jewish world. Mongol period The Caliphate hastened to its end before the rising power of the Mongol Empire. As Bar Hebræus remarks, these Mongol tribes knew no distinction between heathens, Jews, and Christians; and their Great Khan Kublai Khan showed himself just toward the Jews who served in his army, as reported by Marco Polo. Iraq's Jewish community reached an apex in the 12th century, with 40,000 Jews, 28 synagogues, and ten yeshivot, or Rabbinic academies. Jews participated in commerce, artisanal labor and medicine. Under Mongol rule (1258–1335) Jewish physician Sa’ad Al-Dawla served as , or assistant director of the financial administration of Baghdad, as well as Chief Vizier of the Mongol Empire. Hulagu (a Buddhist), the destroyer of the Caliphate (1258) and the conqueror of Palestine (1260), was tolerant toward Muslims, Jews and Christians; but there can be no doubt that in those