The coast of the Kingdom of Granada was a border of importance in Nasrid times and it was also a zone to be protected after the Castilian conquest, mostly against piracy. To control the sea, the successive rulers would build a system of fortresses and watchtowers. The objective of this paper is to apply spatial analysis to the defense system of the southern coasts of Granada and Almeria from the fifteenth to seventeenth century, focusing in its evolution. To achieve this objective, we will use historical documentation and archaeological record as main data for the spatial analysis carried out by a GIS software, mainly visibility and distribution. With this approach we expect to add new insights to this topic and stablish a base for further research and comparison with other neighboring areas of the Kingdom of Granada.