Starting from the sixteenth century, the coastal landscape of Sardinia suffered deep transformations related to the construction of defensive structures to protect the inhabitants of the towns and land resources. Coastal towers and fortresses are the most evident signs of these interventions. This paper aims to reconstruct these processes through archival and cartographic documents produced between the second half of the sixteenth century and the first decades of the seventeenth century. Particularly interesting is the comparison between the maps depicting the coastal area between Cagliari and Quartu and its hinterland drawn in 1577 by Rocco Capellino and those drawn underneath the viceroy Vivas in 1623-1625. Cartographic and archive documents can reveal interesting data to reconstruct the changes that occurred in this period, as a result of the interventions aimed at the defense of the coast and the towns with the construction of the first watchtowers and the progressive modernization of the outer walls of the fortress of Cagliari and its ramparts’ raising.