According to themeparktour.com, crowned king in Germany, Frederick went down to Italy in 1220. And he seemed to be doing everything under the inspiration of the curia, for the purposes that it proposed. He gave dozens of diplomas to Italian bishops who went to solicit him beyond the Alps; he proceeded trained and counseled by a large cohort of Church princes. Having entered Rome, here he proclaims his duty to defend the Church from the arbitrations of the municipalities and to persecute the heretics and issues constitutions for ecclesiastical freedom and the integrity of the faith, he gives other diplomas to the Italian bishops, in which he makes havoc of the statutes citizens and imperial concessions to municipalities. Meanwhile, bishops and prelates were already traveling through Italy as imperial vicars, striking imperial bids, judging disputes between bishops and municipalities, negotiating empire negotiations, imposing peace on cities at war, they provided for ecclesiastical freedoms. Some writers had the vision of an almost identification of the two powers, conforming to the ancient ideal. Certainly, inspired by the Church, implemented or attempted by the emperor, a vast effort of church reaction had taken place which could also compromise the development of the city state and city society, powerless in the face of the alliance of the two supreme powers.
But the course of things was marked by the needs and the nature of the new Italian forces, by the tendency and will of state reconstruction, in the kingdoms and in the cities. Frederick II too soon reappeared as king of Sicily and Puglia, of those lands that he had had to regain at a very young age against the violence and snares of Muslims and German adventurers. And here, after 1220, he immediately turned his effort, certainly benefiting from the prestige that came to him from the imperial crown and from some resource that, then and then, began to come to him from the other lands of the kingdom of Italy, but essentially re-attaching himself to the traditions of Ruggiero II and Guglielmo I, to the Roman, Byzantine and Muslim elements that the South provided him in abundance. The eslegian forces that tended to grow and overflow down there he strongly contained. They were the Arabs of Sicily; it was the clerics who widened the field of their “freedoms”; it was especially the great families that were organizing themselves as a unit, replacing the rules of the Lombard feudal law with those of the Frankish feud, that is, establishing the indivisibility of the succession and the majorasco, in order to better resist the monarchy. The king tamed the Muslims of Sicily and made them military colonies on the mainland; it contained ecclesiastical freedoms; he recalled feudalism to the observance of Norman provisions and issued others. In the practice of government and in the constitutions of the kingdom, published in Melfi, after making peace in San Germano with Pope Gregory IX, he wanted to appear before his subjects the only source of law, exclusive legislator and supreme judge, invested with an absolute power similar to that which the Roman emperor had exercised over the Quirites, after the Quirites had transferred it to the emperor. As in the municipalities of the north and center, the podestà were ex iure romano , so Frederick made himself strong in Roman law.
At the same time that he was carrying out an activity of this kind in the south, Federico was interested in the things of the kingdom of Italy. Could he be estranged from the things of Italy? He had not completely renounced Germany and the countries of upper and middle Italy were like the necessary pillars of this bridge between Sicily and Germany. In the kingdom of Italy, then, the struggles between the cities and the local factions resulted in larger parties to which the two families and the two parties gave occasion, name, nourishment, which in Germany, at the beginning of the century, they had fought for the crown; then, the pope and the emperor, after they returned to new discord. It was not only a need for help and sanctions from above, but an almost instinctive process of idealization of local disputes, all well-defined and almost tangible interests, of free adaptation of municipal life within the framework of the two great universal institutions. The political unity of the peninsula was also expressed in this form: not institutional unity; but, in the middle and above the tiny village factions with various names, in the middle and above the crowd of party leaders or leaders who were beginning to sprout from all sides, two great parties, two flags, two leaders, two myths, which are more particularly municipal, but, to a certain extent, throughout Italy. We must see the new struggles between popes and kings of Sicily, who are also kings of Italy and emperors, in this light too, fermenting from this living substance of Italian soil, nourished by those restless forces of the Italian people: see them at least in function of the nobility that resists the bourgeoisie and of the bourgeoisie that asserts itself on the nobility.