321 and refers to Cologne on the Rhine. These documents stated that Jews could be called to the Curia and owed taxes to Rome, and that Jewish religious leaders were exempt from curial service, signalling that a uniquely Jewish community, prosperous enough to be taxed, had existed in Cologne for some time. During the Carolingian period, Jews had a vital function as importers of goods from the East, and their laws and customs were generally tolerated, although they were not allowed to proselytize to Christians. It was during this peaceful time, that Jews from other communities emigrated to Francia in hopes of better treatment, notably members of the Persian House of Exilarchs, such as Isaac the Jew and Makhir of Narbonne came to Francia and with them, brought a large community of Persian Jews, who later assimilated to European customs. However, these peaceful relations would end with the beginning of the First Crusade and thousands of Jews in communities all along the Rhine were attacked and killed under the presumption that if they were going to attack enemies of the Christ in Jerusalem, they should attack "Christ's enemies" around them in Germany, ushering in a lasting antisemitism that included pogroms, blood libel, and being blamed as the cause of catastrophes like the Black Death and the Mongol invasion of Europe. Despite those difficulties, German Jews continued to practice, refine, and evolve their religious and social customs, including the development of the Yiddish language and an identity as Ashkenazi Jews. They eventually established a uniquely Jewish occupation, working as Court Jews within the Holy Roman Empire. Church laws in the Early Middle Ages Conversions of Jews to Christianity, whether forced or voluntary, during the medieval period were an integral part of the life of Jewish communities in the medieval period. The pressures to convert, other than compulsory baptism to save one's life, could be theological, economic and intellectual. Voluntary conversion by such renegades (meshummadim) was motivated by a number of facts: a change of belief could account for the conversion, as could the desire to marry a Christian or to escape from the restrictions on life as a Jew, or to resecure a livelihood or home. Such conversions proved particularly devastating for the English and Spanish Jewish communities. By the 10th century, most of Europe was under the rule of Christian monarchs who made Christianity the official religion of their realms.