Aeroimage in 1937. Photo archive of the Military Geographical Institute of Serbia
The city was founded by Emperor Justinian I in 535. It existed until 615 and was designed as the seat of the Archbishopric of Justiniana Prima. The arch-priest of the Illyrians ('Ιλλυριών άρχιερεύς) seated in Justinian Prima had jurisdiction over Dacia Ripensis, Dacia Mediterranea, northern Moesia Superior, Dardania, Macedonia Salutaris, Praevalitana and the territory of Bassianae in Pannonia Secunda.  The establishment of the Archbishopric is mentioned in Justinian's own Novel XI from 535, when he promotes the Metropolitan to an Archbishop, independent from the Archbishop of Thessalonica. The establishment is seen as part of the feud between Justinian and the Archbishop of Eastern Illyricum, who was a papal vicar.
The city was to become capital of Illyricum, but Thessaloniki was preferred and Justinian Prima received jurisdiction over the territories of the Diocese of Dacia. Still, the new foundation was not without importance and Justinian made sure that this city, which was one of his favourite projects, received all the necessary support. In 545 Justinian issued another law underlining the episcopal rights and status of Justiniana Prima, which is also confirmed by letters that were exchanged between Justinian and Pope Gregory I at the end of the 6th century.
The city planning combined classical and Christian elements: thermae, a levantine agorai, and streets with colonnades. Typical Eastern Mediterranean features went along with numerous churches.
"He therefore built a wall of small compass about this place in the form of a square, placing a tower at each corner, and caused it to be called, as it actually is, Tetrapyrgia. And close by this place he built a very notable city which he named Justiniana Prima, thus paying a debt of gratitude to the home that fostered him. In that place also he constructed an aqueduct and so caused the city to be abundantly supplied with ever-running water. And many other enterprises were carried out by the founder of this city - works of great size and worthy of especial note. For to enumerate the churches is not easy, and it is impossible to tell in words of the lodgings for magistrates, the great stoas, the fine marketplaces, the fountains, the streets, the baths, the shops. In brief, the city is both great and populous and blessed in every way."
The town was abandoned at around 615. Invading Avars coming from north of the Danube may be one factor, missing political interest in the town after the time of Justinian may be another. Among many other imported finds the presence of 2 pieces of a specific type of fibulae and handmade pottery have been understood as an indication of the presence of Slavs already before the Avar incursion.
The huge correlation between the archaeological site and the description by Procopius as well as finds of seals of the bishop of Iustiniana Prima have determined the identification of Justiniana Prima with Caričin Grad. There have been archaeological excavations for nearly 100 years with the participation of French and more recently also German researchers. There is a permanent exhibition in the national museum in Leskovac. At the site itself monuments there are impressive remains of the fortification, the acropolis as well as of several churches and many other buildings.
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Caričin Grad – Iustiniana Prima, archaeological site - UNESCO