How was Venetian Istria born and under what circumstances? This book takes you inside the diplomatic trenches where the Commune of Venice and the Patriarchate of Aquileia spent over a century arguing, fighting, and bargaining over who would rule over a patch of Istrian communes that had subjected themselves to the Venetian Commune. Drawing on a corpus of previously unedited Latin sources, critically edited and translated here for the first time, this analysis tracks the rival legitimization discourses that each side wielded as diplomatic weapons. From ducal instructions and powers of attorney to pacts, peace treaties, and diplomatic missions, this volume reconstructs the political grammar through which Venetian Istria was forged and legitimized.