The first mention of Jews in Germany is found in two orders of Emperor Constantine (321), in which he regulated the condition of the Jews of Cologne. It is possible that this settlement was of a temporary character, for nothing is heard of the Jews in Germany until the tenth century. A statement to the effect that Charlemagne called Rabbi Kalonymus of Lucca in Italy to be Chief Rabbi of all the Jews of Germany is first reported in the sixteenth century, and is in all likelihood legendary. Under Charlemagne the Jews appear in Germany only as travelling traders. In 1016, however, there was already a bloody persecution of the Jews in Mayence. Gershom ben Judah, a native of France, was rabbi in Mayence. He occupied so prominent a position that he was called ‏‎מאור הגולה‎‏ (light of the exile). He wrote commentaries on various parts of the Talmud, responsa, other Talmudic works, and liturgical poetry. He died in 1028. To him are ascribed various rules, among them a prohibition of polygamy and an injunction to respect the secrecy of letters. At the same time there lived in Mayence Simeon bar Isaac, the liturgical poet, whose hymns are found in the ritual of the German Jews for the second day of Rosh Hashana. In 1090 Emperor Henry IV granted charters to the Jews of Worms and Speyer. These are the oldest laws regulating the status of the Jews in Germany, granting to them freedom of trade and travel, proclaiming the inviolability of their cemeteries, and prohibiting the kidnapping and baptism of their children. Six years later the first crusade broke out, and the mobs composing the army of the crusaders on the Rhine invaded the Jewish settlements, chiefly Cologne, Mayence, Speyer and Worms, in that part of the country. Houses were sacked, synagogues desecrated, and many Jews cruelly murdered; others committed suicide after killing their own children in order to save them from forced conversions. A number of Jews who had been converted to Christianity, in order to save their lives, later on returned to Judaism in spite of the ecclesiastic law which put this under the penalty of death. The Emperor, who at that time was in Italy, sanctioned this in spite of the protests of the Pope.