For much of Italy, the first half of the Quattrocento was a transformative period. As fewer and fewer states came to expand their dominions over larger and larger spaces, the interstices between them were eventually filled up and the polities of the peninsula put in direct competition with each other. In the north, this process brought the Republic of Venice and the Duchy of Milan into conflict over eastern Lombardy – namely the cities and territories of Bergamo, Brescia and Crema. Once the Venetians were finally able to wrest these areas from the Visconti’s grasp, the frontier between two dominions was fundamentally shifted and the political geography of the region redesigned. It was but the final step towards the establishment of Venice’s Terraferma state. The initial product of a larger investigation into the spatial fabric of late medieval Italy, the present article considers the conflicts and peace-making efforts through which Milan and Venice negotiated these profound changes. It does so by examining the text of well-known treaties (such as those of Ferrara and Lodi) alongside several other records from both Milanese and Venetian archives. This is to shed light on the proceedings through which territories were annexed and frontiers moved in late medieval Italy, while also uncovering the range of actors involved, and the series of principles and techniques they adopted to accomplish their goals.