During Late Antiquity, the Eastern Adriatic coast saw an increase in the construction of fortifications through a process we call castellation. Today, we find various archaeological remains from that period, including castrum type fortifications and their associated sacral buildings. Within historiography, the discovered forts along the islands of the Eastern coast of the Adriatic sea, from the Elaphite Islands in the south, to the Veliki Brijuni in the north, most of which were found in the Zadar region, are associated with the time after the ByzantineGothic Wars, in the second half of the 6th century, and the reign of the Byzantine emperor Justinian I. This paper deals with the research of this assumed system, primarily with the processing of island and coastal fortifications, which are considered to be from the period of Justinian’s reconquest. In addition to the processing of these fortifications, this paper also touches on data on other traces of the presumed system of protection of the important navigation routes. The focus of the paper is on the study of the issues brought by the topic, everything from the use of the term limes, it’s meaning, known examples of the limes, changes and innovations during the reign of Emperor Justinian I., the characteristics of the castellation process, the general settings of Justinian’s limes, up to the problems that have arisen during previous research.