To Frederick II. they owed their emancipation. By him Zurich became a free imperial city, governed by its own council. Council and citizens gradually becoming alive to their own civic interests, step by step wrested the civil power from the hands of the Lady Abbess, and emerged into the condition of an independent commonwealth. By this time society within the city had arranged itself into three distinct classes. (1) The clergy, headed by the abbess and the provost. (2) The knights, owing military service to emperor and abbess, and the burghers, or chiefly free landowners, and important commercial men. This second order was the governing class, and out of it came the members of the council. (3) The craftsmen, who exercised their trades only with the permission of their masters, the governing class. The workers were excluded from all share in the government, and were even prohibited from forming guilds. The majority of the artisans and serfs lived without the gates, in the outer city or walled-in suburbs. These political inequalities at length met with violent opposition, and in 1336 there broke out a revolution. The industry of the thrifty and energetic population increased the material wealth of the city, and commercial treaties were entered into with neighbouring countries, with Italy particularly, and Italian influence made itself felt ever since the twelfth century, through four hundred years, not only in trade, but also in architecture. Zurich became an emporium for silk, and the silk manufacture, introduced from Italy, became a speciality, and was found in no other German town.[29] The activity displayed in building churches and monasteries was simply astonishing. The present minster, in the Lombard style, on the type of San Michele at Pavia, was built in the twelfth century, and the abbey was restored by the noble ladies in the thirteenth. The frequent visits of kings and emperors, who held their diets here, naturally increased the importance of the city. Taking it altogether, Zurich must have been, even in the thirteenth century, a fine specimen of a mediæval town, for Barbarossa's biographer, Otto von Freysing, calls it the noblest city of Swabia ("Turegum nobilissimum Sueviae oppidum").[30] Her policy of entering into alliances with the Swabian and Rhenish towns, and with the vast South-German coalition, and the friendly political and commercial relations she maintained, show that she fully grasped the situation, and gave her that security which promoted her trade and industry, and allowed her to develop freely.