Of the northern states only three deserve special mention [Sidenote: Genoa.] at this time. Genoa, isolated in the north-western corner and surrounded by mountains, plays a very slight part in the general history of Italy, though it has some considerable importance as commanding the direct route from Provence to the peninsula. The energies of its citizens were mainly absorbed in the acquisition of wealth by eastern trade, in maintaining wars with Pisa and Venice, and in the incessant feuds of the great families of Doria and Spinola. Milan, which had long held a predominant position among [Sidenote: Milan.] the Lombard towns, was already beginning to lose its republican independence. There, as in Florence, class divisions were mixed up with the quarrels of factions. In 1259 the Guelf leader, Martino della Torre, headed the citizens in a successful struggle against the Ghibelline nobles, and took advantage of his victory to assume the lordship of the city. The neighbouring towns of Lodi, Como, Vercelli, and Bergamo fell one after another under the rule of the Della Torre. But in 1277 a revolution was effected by the Ghibellines under the Archbishop of Milan, Otto Visconti, to whom the lordship of the city was transferred, and from whom it passed on his death in 1295 to his nephew Matteo Visconti, the ancestor of the later dukes of Milan. But the Visconti dynasty was not yet permanently established, and in 1302 a Guelf league was formed among the chief Lombard towns which forced Matteo to withdraw, and Guido della Torre became the ruler of Milan. Venice, the last of the important northern states, was even [Sidenote: Venice.] more isolated from Italy than Genoa, both by geography and by its absorbing interests in the Levant. The overthrow of the Greek Empire in 1204 had given Venice a commanding position in the east, but the restoration of 1261 had raised a very formidable rival in Genoa, and for more than a century the two republics were engaged in a series of costly and exhausting wars. But the main interest of Venetian history at this time lies in the building up of that oligarchical constitution which gave to Venice a vigour and consistency of political action quite unique in Italy, and enabled her in the fifteenth century to establish a very formidable power on the mainland.