Moesia Prima (/ˈmiːʃə/, /ˈmiːsi.ə/, or /ˈmiːʒə/; Latin: Moesia; Greek: Μοισία) was a frontier province of the late Roman Empire, situated in the central parts of present-day Serbia, along the south bank of the Danube River. Provincial capital was Viminacium, near modern Kostolac in Serbia).
Province of Moesia Prima was created at the end of the 3rd century during administrative reforms of roman emperor Diocletian (284–305) who divided the Province of Moesia Superior in two separate provinces: Moesia Prima to the north and Dardania to the south.
Sometime in 293–294, emperor Diocletian traveled through Moesia Superior and came to its capital Viminacium. During that visit he created new province under the name Moesia Superior Margensis or Moesia Prima. The term Margensis was used in reference to the name of Margus River that runs through the province. Emperor also registered that the inhabitants of province wrote in Latin, as opposed to Greek in the southern regions.
At first, Province of Moesia Prima belonged to the Diocese of Moesia. Probably under emperor Constantine I (306–337), the Diocese of Moesia was split in two, forming the Diocese of Dacia in the north and Diocese of Macedonia in the south. Province of Moesia Prima became part of Diocese of Dacia, that belonged to the Praetorian prefecture of Illyricum.
The emperor Jovian (363-364) who reestablished Christianity as the official religion of the Roman Empire was born in Moesia Prima, in Singidunum. In his early career, later roman emperor Theodosius I served as military commander of Moesia Prima in 373. In 382 roman emperors Theodosius I and Gratian met in Viminacium, the capital of Moesia Prima, during the Gothic Wars.
Danubian border of Moesia Prima was protected by fortifications of the Limes. Two roman legions were stationed in the province: Legio IV Flavia Felix in Singidunum and Legio VII Claudia in Viminacium. The seat of Praefectus legionis septimae Claudiae was in the frontier fortress of Cuppae (Golubac, Serbia).
As a frontier province, Moesia Prima was under constant threat of barbaric invasions. In the middle of 5th century the province was devastated by the Huns of Attila who took Singidunum and Viminacium in 441. The province was later invaded by various Germanic tribes like Ostrogoths, Gepids, Heruli and others.
Major efforts to secure the province were undertaken in the time of Justinian I (527–565) who rebuilt Viminacium and Singidunum around 535, restoring the frontier fortresses to their former military importance. Throughout the 6th century, Moesia Prima was often invaded by Slavs. Province was also invaded bu the Avars who took Singidunum and Viminacium during the war of 582-584. During emperor Maurice's military campaigns against Avars and Slavs, Moesia Prima served as a base of military operations.
After the fall of emperor Maurice in 602, Byzantine defenses in Moesia Prima finally collapsed. At the very beginning of 7th century, Avars and Slavs sacked and burned Singidunum and Viminacium to the ground and the interior of the fallen province Moesia Prima was finally settled by the Slavic Serbs.
The chief towns of Moesia Prima were: Viminacium (sometimes called municipium Aelium; modern Kostolac) and Singidunum (Belgrade).