Soon after his settlement in Musso, Il Medeghino, wishing to secure the gratitude of the Duke, his master, began war with the Grisons. From Coire, from the Engadine, and from Davos, the Alpine pikemen were now pouring down to swell the troops of Francis I.; and their road lay through the Lake of Como. Il Medeghino burned all the boats upon the lake, except those which he took into his own service, and thus made himself master of the water passage. He then swept the ’length of lordly Lario’ from Colico to Lecco, harrying the villages upon the shore, and cutting off the bands of journeying Switzers at his pleasure. Not content with this guerilla, he made a descent upon the territory of the Trepievi, and pushed far up towards Chiavenna, forcing the Grisons to recall their troops from the Milanese. These acts of prowess convinced the Duke that he had found a strong ally in the pirate chief. When Francis I. continued his attacks upon the Duchy, and the Grisons still adhered to their French paymaster, the Sforza formally invested Gian Giacomo de’ Medici with the perpetual governorship of Musso, the Lake of Como, and as much as he could wrest from the Grisons above the lake. Furnished now with a just title for his depredations, Il Medeghino undertook the siege of Chiavenna. That town is the key to the valleys of the Spluegen and Bregaglia. Strongly fortified and well situated for defence, the burghers of the Grisons well knew that upon its possession depended their power in the Italian valleys. To take it by assault was impossible, Il Medeghino used craft, entered the castle, and soon had the city at his disposition.