In the Ottoman regency, the fortifications of Algiers evolve according to the politico-economic growth experienced by the city partly thanks to the development of the maritime piracy and the lusts it entails. Its stranglehold on the sea, arouses many projects of punitive expeditions. The construction of fortifications is then the major concern of its new leaders who between the sixteenth and the seventeenth centuries, fortify the city, its bay and the hinterland. These efforts develop over the three centuries of the Ottoman regency, a singular military architecture for the city of Algiers. The sixteenth century sees, a medieval reminiscence with the first fortifications, then, with the presence of Christians, a western influence the seventeenth century and the arrival of the Moriscos, brings a second breath to this defensive typology which is defined as a local style between domestic and military architecture. The question is: why Algiers has developed a particular defensive typology while the modernization of the artillery had led to an internationalization of the defensive system.