Fortification architecture represents a relevant segment of the cultural heritage of any historical epoch because its shaping and concept are under the influence of all the elements and factors responsible for global development of any society. Numerous settlements on the teritory under observation show continuity in building fortifications to begin with the protourban through Hellenic and Roman till the late antiquity and they show the transformation usually related to the change of cultural and ethnic basis. In that context the most significant remains of the fortification structures are in Kurik, Apsor, Jader, Aseria, Varvaria, Salona, Narona and Ljes. The least known are the fortifications of the cities which under the Roman administration abandon elevated position of the hill-fort and descend onto the foothill which is the case of most cities in Kvarner Bay and those situated under the Velebit mountain. In them some smaller segments of prehistorical and late antiquity defense structures put the existence of similar Roman structures in question. Particular problem in reconstruction of the change sequence on city walls results from the total and intentional devastation which were fate of Tarsatika, Arba, Senia, Argirunt, Epidaur, Budva and Bar fortification. To study chronology of origin and changes on the Roman city walls besides the epigraphic and other material remains the knowledge of building tecniques and defense innovations introduced by the war technology development is fundamental. The basic building material was stone which also defines building techniques suited to it. On the observed teritory the predominant technique was opus quadratum which was the result of the historical heritage and adds to the thought that almost all, the Roman cities included, had a long tradition of fortifying. The Roman innovation of opus incertum is present mainly as a result of newly built segments and subsequent adaptations. The development of war machines inspired the creativity in building the city fortifications which get additional towers, buttresses, parallel walls, transversal walls (diatichism), and outter walls (bulwark)-protychisms. The analysis of the accessible material and the recent research with on site autopsy show more complex changes as opposed to the data from the literature. Numerous situations which can be a subject-matter of a dissertation are pointed out and possible options based on available knowledge have been offered. Special problems are the interpretations of the double walls in Tarsatica and Kurik, the existence of diatichism in Apsor and Narona, dating of propugnaculum in Jader and Salona as well as defining the development stages in Varvaria, Aseria and Ljes.