During the Christian era, the first towers were built in proximity to the coasts under threat of being raided by Saracen pirates and, subsequently, also by Barbary corsairs. Around 1570, the Crown of Spain decided to intervene with a defence plan that would result in the construction of a coastal line of watchtowers. In order to raise the necessary funds, a specific tax was imposed on all Sardinian villages, even those far from the coast, in proportion to the benefits that the populations could gain from protection against raids and invasions. The Sardinian coastal defence system remained operational up until 1867. Some of the towers underwent substantial work in order to adapt them for use by customs officials. Others, particularly in the archipelago of La Maddalena, were converted into batteries for strategic control of the Mediterranean, a role that they continued to perform even after the First World War. During the Second World War, many towers were put back into operation as lookout points. The Tower of Vignola was built in 1572 to guard an area of tuna-fishing nets. It was built into a truncated cone shape with a base measuring 12 m in diameter.