In the 15th century, the Turkish growing threat represented one of the greatest concerns for the western monarchs, since piracy was part of the sea policy of these people. As a matter of fact, pirates were obliged to share their spoils with the government: therefore, this activity represented for the latter one of the greatest incomes. Moreover, pirates did not limit themselves to assault ships, but they also carried out raids in the inland. These raids went on, although they were less intense, for the whole 18th century.
(the following links lead to Italian texts)
Towers open to the public