The book explores the history of Justiniana Prima, a city built by Emperor Justinian I (527-565) in his birthplace near Niš in present-day Serbia. Previous studies focused on determining the city’s location, underestimating the significance of analysing written sources for the reconstruction of this city’s genesis and importance. Using the information from Emperor Justinian’s Novels XI and CXXXI, as well as Book IV of Procopius of Caesarea’s De aedificiis, the author endeavours to show that Justiniana Prima’s historic significance resulted from granting its Church the status of an archbishopric with its own province in 535, which was independent of Rome. Justinian wanted to introduce profound changes to the ecclesiastical organisation based on the state law.