Such was the rise and growth of the Jewish colonies in Poland. As time went on, the commercial intercourse between these colonies and the West led to a spiritual relationship between them and the centers of Jewish culture in Europe. A contemporary Bohemian scholar of the Tosafist school, Rabbi Eliezer, informs us that the Jews of Poland, Russia, and Hungary, having no scholars of their own, invited their spiritual leaders from other countries, probably from Germany. These foreign scholars occupied the posts of rabbis, cantors, and school teachers among them, and were remunerated for their services. At the same time studious Polish Jews were in the habit of going abroad to perfect themselves in the sciences, as was also the case with the Jewish settlers in Russia. From the German mother country the Polish Jews received not only their language, a German dialect, which subsequently developed into the Polish-Jewish jargon, or Yiddish, but also their religious culture and their communal organization. All this, however, was in an embryonic stage, and only gradually unfolded in the following period. 2. THE CHARTER OF PRINCE BOLESLAV AND THE CANONS OF THE CHURCH The importance of Jewish immigration for the economic development of Poland was first realized by the feudal Polish princes of the thirteenth century. Prompted by the desire of cultivating industrial activities in their dominions, these princes gladly welcomed settlers from Germany, without making a distinction between Jews and Christians. Nor did the native Slav population suffer inconvenience from this immigration, which, on the contrary, brought the first elements of a higher civilization into the country. In a land which had not yet emerged from the primitive stage of agricultural economy, and possessed only two fixed classes, owners of the soil and tillers of the soil, the Jews naturally represented the "third estate," acting as the pioneers of trade and finance. They put their capital in circulation, by launching industrial undertakings, by leasing estates, and farming various articles of revenue (salt mines, customs duties), and by engaging in money-lending. The native population, which medieval culture, with its religious intolerance and class prejudice, had not yet had time to "train" properly, lived at peace with the Jews.