system. The proof of this was, that while vindicating their rights as
towns, the free cities never questioned the validity of the imperial
title. Even after the peace of Constance in 1183, when Frederick
Barbarossa acknowledged their autonomy, they received within their
walls a supreme magistrate, with power of life and death and ultimate
appeal in all decisive questions, whose title of Potesta indicated
that he represented the imperial power--Potestas. It was not by the
assertion of any right, so much as by the growth of custom, and by the
weakness of the Emperors, that in course of time each city became a
sovereign State. The theoretical supremacy of the Empire prevented any
other authority from taking the first place in Italy. On the other
hand, the practical inefficiency of the Emperors to play their part
encouraged the establishment of numerous minor powers amenable to no
controlling discipline.

The free cities derived their strength from industry, and had nothing
in common with the nobles of the surrounding country. Broadly
speaking, the population of the towns included what remained in Italy
of the old Roman people. This Roman stock was nowhere stronger than in
Florence and Venice--Florence defended from barbarian incursions by
her mountains and marshes, Venice by the isolation of her lagoons. The
nobles, on the contrary, were mostly of foreign origin--Germans,
Franks, and Lombards, who had established themselves as feudal lords
in castles apart from the cities. The force which the burghs acquired
as industrial communities was soon turned against these nobles. The
larger cities, like Milan and Florence, began to make war upon the
lords of castles, and to absorb into their own territory the small
towns and villages around them. Thus in the social economy of the
Italians there were two antagonistic elements ready to range
themselves beneath any banners that should give the form of legitimate
warfare to their mutual hostility. It was the policy of the Church in
the twelfth century to support the cause of the cities, using them as
a weapon against the Empire, and stimulating the growing ambition of
the burghers. In this way Italy came to be divided into the two
world-famous factions known as Guelf and Ghibelline. The struggle
between Guelf and Ghibelline was the struggle of the Papacy for the
depression of the Empire, the struggle of the great burghs face to
face with feudalism, the struggle of the old Italie stock