The rumor of the existence of an independent Jewish community in the land of the Chazars, which had penetrated to Spain, roused his interest. Eldad's appearance in Spain, several decades before Chasdaï's birth, had given probability to the vague tradition, but, on the other hand, rendered it improbable through the exaggeration that the ten tribes were still in existence in all their strength. Chasdaï never failed to make inquiries about a Jewish kingdom or a Jewish ruler when embassies came to him from far or near. The news of a Jewish community in the land of the Chazars, which he received from ambassadors from Khorasan, was very welcome to him, especially when he learnt that a Jewish king was on the throne there. He now heartily wished to enter into communication with this king. He rejoiced when the news was confirmed by the Byzantine ambassadors, who gave him the additional information that the reigning king of the Chazars was called Joseph, and that they were a powerful and warlike nation. This information served only to increase his desire to enter into close communication with the Jewish kingdom and its ruler. He therefore sought a trustworthy messenger who could take charge of his letter of homage, and at the same time bring back further particulars. After several vain attempts, he succeeded in effecting the desired communication. In an embassy of the Slavonic king from the Lower Danube there were two Jews who had to act as interpreters in Cordova. Chasdaï gave the Slavonic ambassadors a letter to the king of the Chazars. This letter, in beautiful Hebrew prose, with introductory verses, written by Menachem ben Saruk, is a priceless document for the history of the time. The author, in his pious wishes and in his humble bearing, skilfully permitted his statesmanship and a sense of his own worth to be seen. Chasdaï's letter fortunately reached the hands of King Joseph, through the instrumentality of a man Jacob ben Eleazar from the land of Nemes (Germany). Joseph was the eleventh Jewish prince since the time of Obadiah, the founder of Judaism in that country. The country of the Chazars even at that time (960) still possessed great power, although it had already lost several districts or feudatory lands. The residence of King Joseph was situated on an island in the Volga, and included a golden tent-like palace having a golden gate. The kings had to oppose the Russians, who had become more powerful since the immigration of the Waragi, and who had always coveted the fruitful country of the Chazars. They found it necessary to keep a standing army so as to be able to attack the enemy at a moment's notice. In the tenth century there were 12,000 regular soldiers, partly cavalry, provided with helmets and coats of mail, and partly infantry armed only with spears. The decaying Byzantine empire was forced to respect the kingdom of the Chazars as a great power, and to recognize the Jewish ruler as "the noble and illustrious king." Whilst the Byzantine emperors used to seal their diplomatic letters to the Pope and to the Frankish emperors with a golden bull of light weight (two solidi), they made it one-third heavier when they wrote to the kings of the Chazars. Whoever is acquainted with the pedantic etiquette of this unstable court will at once recognize how much of fear was expressed by this mark of honor. The Chazar kings took great interest in their foreign co-religionists, and made reprisals for wrong done to the Jews. The king expressed his joy at receiving Chasdaï's letter, and corrected the false impression that the land of the Chazars had always been inhabited by Jews. "The Chazars were rather of heathen origin," he wrote in his answer, and narrated how his great ancestor Bulan had been converted to Judaism. He went on to enumerate the successors of Bulan, all of whom had Jewish names. He then describes the extent of his dominions, and the various peoples that were subject to him. As regards the hopes of a Messianic redemption which he also cherished, he remarks that neither he nor his people knew anything definite. "We set our eyes upon Jerusalem," he says, "and also upon the Babylonian schools. May God speedily bring about the redemption." "You write," he says, "that you long to see me. I have the same longing to make the acquaintance of yourself and your wisdom. If this wish could be fulfilled, and I might speak to you face to face, you should be my father and I would be your son, and I would entrust the government of my state to your hands."

When Joseph wrote this letter, he could boast of the peaceful state of his kingdom. But circumstances changed in the course of a few years. One of Rurik's descendants, the Russian Prince Sviatislav of Kief, formerly almost a subject of the Chazars, made a formidable attack upon the country, and captured the fortress of Sarkel (965). The conqueror grew more powerful, and, a few years later, in 969, the same Sviatislav took the capital, Itil (Atel), and also captured Semender, the second town of the Chazars. The Chazars took to flight, some going to an island in the Caspian Sea, others to Derbend, and yet others to the Crimea, in which many members of the same race lived, and which henceforth received the name of "the Land of the Chazars." Its capital was Bosporus (Kertch). Thus did the kingdom of the Chazars decline, and Joseph was its last king who possessed any power. When Chasdaï received his letter, his patron, Abdul-Rahman, had died. His son Alhakem, a more zealous patron of science and poetry even than his father, now sat upon the throne. More peacefully disposed than his father, he honored Chasdaï, whom he made an important state official, and whose superior talents he employed as freely as his father had done.

Imitating the example of two Caliphs, who respected genius, Chasdaï protected the Jews, and to him is credit due for having given the impulse to the Jewish-Andalusian culture. He gathered around him at Cordova a band of talented philosophers and poets, who in turn immortalized him in their works and poems. "In Spain far and wide, wisdom was cherished in Chasdaï's time. His praise was sung by eloquent tongues." Only two of the philosophers and poets of this time became famous, Menachem ben Saruk and Dunash ben Labrat. Both of these made the Hebrew language, which they considerably enriched, the object of deep research. They went far beyond all their predecessors that had worked at philology, the Karaites and even Saadiah.

Dunash ben Labrat in his works developed a symmetry and harmony of expression in the holy language such as was scarcely conceivable by his predecessors. He was the first to employ meter in Hebrew poesy, which he made melodious through the introduction of the strophe. Dunash was blamed by Saadiah for this as though he had made an unheard-of innovation. Saadiah thought that violence was done to the Hebrew language thereby. However, the new Hebrew poetry was enriched through the efforts of the Jewish-Andalusian writers. Hitherto, poetical compositions had been of a synagogal character, always gloomy, and never assuming a joyful tone. Even hymnal poetry was not devoid of this characteristic, and continued halting and rugged like Kaliri's. In didactic and controversial poems a miserable doggerel was used, as in the verses of Solomon ben Yerucham, of Abu-Ali Jephet, of Ben-Asher and Sabbataï Donnolo. Chasdaï, however, gave the poets an opportunity of changing their subjects. His imposing person, his high position, his deeds, and his princely liberality had an inspiring influence upon the poets, and whilst they sang his praises in animated strains, they breathed new life into the apparently dead Hebrew language, rendering it harmonious and capable of development. Of course, the Jewish-Andalusian poets took the Arabs as their model. They in truth do not deny that "Arab became the teacher of Eber." But Dunash and others, who imitated him, did not slavishly adhere to their Arab pattern, nor adopt its unnatural meter, but they selected its beauties and imitated them. The verses at the beginning of this flourishing period of poetry were brisk and lively in their measure, and yet the Hebrew poetry of the epoch of Chasdaï did not entirely cast off its fetters, nor change its high-flown style. "The poets in Chasdaï's time first began to chirp," as the inimitable critic of a later time remarks. The favorite themes of the new Hebrew poesy now became panegyric and satire, but it did not lose sight of liturgical poetry, which it also adorned with the beauty of meter.

Little is known of the life and character of the first two founders of the Andalusian-Jewish culture. As far as can be gathered from existing sources, Menachem ben Saruk, of Tortosa (born 910, died 970), was in needy circumstances from his earliest years; at any rate, his patrimony was too small to maintain him. Chasdaï's father Isaac was interested in him, and took care that pecuniary difficulties should not destroy the germ of poetry which was latent in him. His favorite occupation was the study of the Hebrew language; he made use of the works of his predecessors, but he did not acquire his noble Hebrew style from them—that was inborn.

When Chasdaï attained his high position, he invited the favorite of his father, with flattering words and glowing promises, to come to Cordova. Menachem became Chasdaï's court poet, and was warmly attached to him, praising him in every kind of verse, and, as he himself affirms, "exhausted poetry in singing Chasdaï's praises." Chasdaï encouraged him to write on the philology of the Hebrew language, and to endeavor to ascertain its various forms, and to investigate the meanings of words. Menachem in consequence wrote a complete Hebrew dictionary (Machbereth), with some grammatical rules, in which he corrected his predecessors in many respects. Brought up amidst surroundings by which harmonious and impressive speech was prized, the grammarian of Tortosa valued language in general very highly, and the Hebrew language in particular, and it was the aim of his work to discover the peculiar refinements of this language. Menachem ben Saruk was the first to distinguish clearly the pure roots in the Hebrew language, and to separate them from the formative prefixes and suffixes—a theory which now appeared for the first time, and which had been misapprehended by previous grammarians. This misapprehension, indeed, had led them into using malformed and ill-sounding words in their verses. Menachem, in his lexicographical work, puts the various forms under each root, and often expounds their meanings with surprising clearness and nicety. In cases where he gives a peculiar explanation according to his understanding of the Biblical verse, he often shows healthy thought and refined taste, and there is a marked step forward in exegesis from Saadiah to Menachem. Now and again he gave explanations which were opposed to Talmudic tradition and the ideas of the time. His lexicographical work was much read and used, because it was written in Hebrew. It found its way into France and Italy, supplanted the works of Saadiah and the Karaites, and, for a long time, was the guide-book for Bible expositors. But grand and flowing as Menachem's Hebrew prose is, his verse is unattractive and awkward; he did not understand how to handle Hebrew meter. He was, however, supplemented by his rival, Dunash ben Labrat.

This poet (also called Adonim) came from Bagdad, and was younger than Menachem (born 920, died 970). He afterwards lived in Fez, and was likewise invited to Cordova by Chasdaï. Dunash appears to have been wealthy, and was thus able to be freer and more independent than the grammarian of Tortosa. He was a man of spirited and reckless disposition, who did not weigh his words, and was well qualified for literary controversy. He, too, possessed a deep knowledge of the Hebrew language, and was a far more successful poet than Menachem. As has been mentioned, he was the first of the Rabbanite circle in Spain to introduce meter into the new Hebrew poetry, to which he thereby gave a fresh charm. He was, however, bold and venturesome. He criticised Saadiah's exegetical and grammatical works in a polemic (Teshuboth), assuming rather a harsh tone, although he was personally acquainted with the author, and was perhaps his pupil. As soon as Menachem's dictionary reached him, Dunash determined to write an unsparing criticism of it, and to bring its mistakes to light. His review was witty but scornful. Dunash did not keep within the limits of scientific discussion, but used it to promote his own interests. He dedicated his critical works against Menachem to the Jewish statesman, whom he flattered so abjectly in some prefatory verses, that we can hardly fail to see that his object was to gain over the Jewish Mæcenas to his side, and to injure Menachem in the eyes of the latter.

Dunash's flattery of the Jewish statesman and his coarse polemic against Menachem are not wanting in power. The admiration of Chasdaï for Ben-Saruk was diminished when he perceived that Dunash was a better poet, and at least as good a philologist. When various calumniators who wished to ingratiate themselves with the Jewish prince, traduced Menachem before him, Chasdaï's favor was withdrawn from the latter, and changed into direct hostility. In what their defamations consisted is not known.

Menachem appears to have died before his rival Dunash, and his pupils undertook to justify him. Jehuda ben Daud, Isaac Ibn G'ikatilia, and Ben-Kafren (Ephraim) were the most important of these. They, too, dedicated their polemical writings to the Jewish minister, and sent him a panegyric and a satire against Dunash. Chasdaï seems to have just returned from a diplomatic victory which he had won for the Caliph Alhakem. The followers of Menachem celebrated his triumph: "The mountains greet the protector of learning, the prince of Judah. All the world rejoices at his return, for whenever he is absent, darkness sets in, the haughty rule and fall upon Judah's sons. But Chasdaï brings back peace and order. God has appointed him prince, and granted him the king's favor, whereby He exalted him above all the nobles."

Menachem's defenders endeavored to appeal to Chasdaï's love of truth, and to make him the arbiter against Dunash, "who set himself up as the chief of commentators, who knows neither law nor limit of change, and who desecrates and spoils the holy language through his foreign meter." The study of the Hebrew language was carried on in Spain by means of severe contention and virulent satire. The pupils of Dunash continued the quarrel. The followers of Menachem and Dunash hurled witty lampoons against each other, which fact contributed largely towards making the Hebrew language at once pliant and rich.