The Eastern Adriatic, and most especially its coast along with its archipelago, saw during Late antiquity an important surge in the building of fortifications. This period saw the construction of a somewhat new type of fortified settlements referred to as castra. This phenomenon has in the scientific literature mostly been brought into connection with the rule of Byzantine emperor Justinian I and his so-called reconquest. Thus, this work focuses on the microregion of Northern Dalmatia presenting the cases of 14 castra which are: Gradina and Gustjerna, both on the Island of Žirje, St. Michael’s fortress in Šibenik, Tureta on the Island of Kornat, Gradina on the Island of Vrgada, Pustograd and the castrum on the Ćokovac hill, both on the Island of Pašman, St. Michael’s fortress on the Island of Ugljan, the town of Zadar, the castrum on the Islet of Veliki Sikavac, castrum St. George above the city of Pag and the castrum above the Caska bay, the castrum on the peninsula of Svetojanj, also on the Island of Pag, the castrum on cape Gradina near Modrič Drage and finally the castrum near Tribunj-Šibuljina both on the slopes of the sub-Velebit region. This work also addresses the issue of Early Byzantine castra in the northern Dalmatian hinterland with the cases of the settlement of Varvaria and Asseria and the castrum of Čuker near Mokro Polje, as well as the settlement of Knin. For every castrum, information is provided on the actual state of archaeological researches on the site, the configuration and conception of the fortifications and other archaeological finds on the site. Based on this account and the works of various scholars, this paper discusses the main characteristics of these castra as well as debating the existence of an Early Byzantine defensive system on the Eastern Adriatic coast, known in the literature as the Maritime limes, while presenting scientific views challenging this assertion.