In the year 1443 Colleoni quitted the Venetian service on account of a quarrel with Gherardo Dandolo, the Provoditore of the Republic.  He now took a commission from Filippo Maria Visconti, who received him at Milan with great honour, bestowed on him the Castello Adorno at Pavia, and sent him into the March of Ancona upon a military expedition.  Of all Italian tyrants this Visconti was the most difficult to serve.  Constitutionally timid, surrounded with a crowd of spies and base informers, shrinking from the sight of men in the recesses of his palace, and controlling the complicated affairs of his Duchy by means of correspondents and intelligencers, this last scion of the Milanese despots lived like a spider in an inscrutable network of suspicion and intrigue.  His policy was one of endless plot and counterplot.  He trusted no man; his servants were paid to act as spies on one another; his bodyguard consisted of mutually hostile mercenaries; his captains in the field were watched and thwarted by commissioners appointed to check them at the point of successful ambition or magnificent victory.  The historian has a hard task when he tries to fathom the Visconti’s schemes, or to understand his motives.  Half the Duke’s time seems to have been spent in unravelling the webs that he had woven, in undoing his own work, and weakening the hands of his chosen ministers.  Conscious that his power was artificial, that the least breath might blow him back into the nothingness from which he had arisen on the wrecks of his father’s tyranny, he dreaded the personal eminence of his generals above all things.  His chief object was to establish a system of checks, by means of which no one whom he employed should at any moment be great enough to threaten him.  The most formidable of these military adventurers, Francesco Sforza, had been secured by marriage with Bianca Maria Visconti, his master’s only daughter, in 1441; but the Duke did not even trust his son-in-law.  The last six years of his life were spent in scheming to deprive Sforza of his lordships; and the war in the March, on which he employed Colleoni, had the object of ruining the principality acquired by this daring captain from Pope Eugenius IV. in 1443.

Colleoni was by no means deficient in those foxlike qualities which were necessary to save the lion from the toils spread for him by Italian intriguers.  He had already shown that he knew how to push his own interests, by changing sides and taking service with the highest bidder, as occasion prompted.  Nor, though his character for probity and loyalty stood exceptionally high among the men of his profession, was he the slave to any questionable claims of honour or of duty.  In that age of confused politics and extinguished patriotism, there was not indeed much scope for scrupulous honesty.  But Filippo Maria Visconti proved more than a match for him in craft.  While Colleoni was engaged in pacifying the revolted population of Bologna, the Duke yielded