As the Mahometan empire grew in size, the activity of its Jewish inhabitants increased in proportion. The first Caliphs of the house of Ommiyyah, by reason of their continual wars with the descendants and comrades of Mahomet, with the fanatical upholders of the letter of the Koran, and with the partisans of the spiritual Imamate (high-priesthood), had become entirely free from that narrow-mindedness and mania for persecution which characterized the founder and the first two Caliphs. The following rulers of the Mahometans, Moawiyah, Yezid I., Abdul-Malik, Walid I., and Suliman (656-717), were far more worldly than spiritual; their political horizon was extensive, and they fettered themselves but little with the narrow precepts of the Koran and the traditions (Sunna). They loved Arabic poetry (Abdul-Malik was himself a poet), held knowledge in esteem, and rewarded the author quite as liberally as the soldier who fought for them. The Jewish inhabitants of Mahometan countries soon adopted the Arabic language. It is closely related, in many of its roots and forms, to Hebrew, with which language all of them were more or less familiar, and they needed a knowledge thereof, as it was the indispensable medium of communication. The enthusiasm which the Arabs felt for their language and its poetry, the care which they took to keep it pure, accurate and sonorous, had their effect upon the Jews, and taught them to employ correct forms of speech. During the six hundred years which had elapsed since the fall of the Jewish nation, the Jews had lost the sense of beauty and grace of expression; they were negligent in their speech, careless of purity of form, and indifferent to the clothing of their thoughts and emotions in suitable terms. A people possessed of an imperfect delivery, using a medley of Hebrew, Chaldee, and corrupt Greek, was not in a position to create a literature, much less to enchain the wayward muse of poetry. But, as already mentioned, the Jews of Arabia formed an exception. They acquired from their neighbors correct taste, and the art of framing their speech pleasantly and impressively. The Jewish tribes of Kainukaa and Nadhir, which had emigrated to Palestine and Syria, the Jews of Chaibar and Wadil-Kora, who had been transplanted to the region of Kufa and the center of the Gaonate, brought with them to their new home this love and taste for the poetical Arabic tongue, and gradually instilled them into their co-religionists. Hardly half a century after the occupation of Palestine and Persia by the Arabs, a Babylonian Jew was able to handle the Arabic language for literary purposes: the Jewish physician, Messer-Jawaih of Bassorah, translated a medical work from the Syriac into Arabic. Henceforward the Jews, together with the Syrian Christians, were the channels through which scientific literature reached the Arabs.