It was not long before their influence began to manifest itself, first in Northern Italy, and later in the south and center. The north Italian poets began to imitate the troubadours, and soon a considerable body of poetry had been composed by native poets, in the manner and--a phenomenon worthy of note--in the language itself of the Provençal poets. This is due to the relationship between the dialects of Northern Italy and the Provençal, and also to the fact that at that time the latter tongue was far more elegant and cultivated than the other Romance languages. This north Italian poetry is always included in the Provençal collections and the writers are known as troubadours in spite of their Italian nationality. Among the most famous are Bartolomeo Zorzi of Venice, Bonifaccio Calvo of Genoa, and especially Sordello of Mantua, praised by Dante in a famous passage of the Purgatory, and the subject of Browning's well-known poem. We see, then, that the above poets belong rather to the history of Provençal than that of Italian literature. To find the first springs of national poetry in Italy, we must traverse the whole length of the peninsula and arrive at the court of Frederick II. (1194-1250) in Sicily, which at this time was far ahead of the rest of the country in civilization, art, and literature. Frederick himself was a many-sided man, warrior, statesman, lawyer, and scholar, and stands out among his contemporaries, especially in matters of religious tolerance. He welcomed to his court not only the scholars, poets, and artists of Europe, but likewise Arabs, who were at that time in possession of a high degree of culture. He caused many Greek and Arab authors to be translated into Latin, among them Aristotle; he founded the University of Naples; above all, by his own mighty personality, he made a deep impression on the times. Frederick's ministers were, like himself, men of culture and learning. Chief among them was Pier delle Vigne, statesman and poet, the cause of whose tragic death by his own hand is told by Dante in the Inferno. The influence of the troubadours made itself felt in Sicily about the same time as in Northern Italy, only here the imitation was in the Italian language and not in Provençal. Among the early Sicilian poets who wrote after the manner of the troubadours, was the Emperor Frederick II. himself, his son, Enzio, and Pier delle Vigne. From an æsthetic point of view, this early indigenous poetry is of little interest, but as the beginning of a movement which culminated in the New Life and Divine Comedy of Dante, it is of very great importance.