Thracia was the name of a province

Roman province

In Ancient Rome, a province was the basic, and, until the Tetrarchy , largest territorial and administrative unit of the empire's territorial possessions outside of Italy...

 of the Roman empire

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

. It was established in AD 46, when the former Roman client state of Thrace

Thrace

Thrace is a historical and geographic area in southeast Europe. As a geographical concept, Thrace designates a region bounded by the Balkan Mountains on the north, Rhodope Mountains and the Aegean Sea on the south, and by the Black Sea and the Sea of Marmara on the east...

 was annexed by order of emperor Claudius

Claudius

Claudius , was Roman Emperor from 41 to 54. A member of the Julio-Claudian dynasty, he was the son of Drusus and Antonia Minor. He was born at Lugdunum in Gaul and was the first Roman Emperor to be born outside Italy...

 (ruled 41-54).

Under the administrative reforms of Diocletian

Diocletian

Diocletian |latinized]] upon his accession to Diocletian . c. 22 December 244  – 3 December 311), was a Roman Emperor from 284 to 305....

 (ruled 284-305), Thracia's territory was divided into four smaller provinces, Thracia, Haemimontus, Rhodope

Rhodope (Roman province)

Rhodope was a late Roman and early Byzantine province, situated on the northern Aegean coast. A part of the Diocese of Thrace, it extended along the Rhodope Mountains range, covering parts of modern Western Thrace and south-western Bulgaria. The province was headed by a governor of the rank of...

and Europa

Europa (Roman province)

Europa was a Roman province within the Diocese of Thrace. Established by Roman Emperor Diocletian in 314, the province's capital was Perinthus. The province largely corresponds to what is modern day European Turkey...

. These belonged to the diocese

Roman diocese

A Roman or civil diocese was one of the administrative divisions of the later Roman Empire, starting with the Tetrarchy. It formed the intermediate level of government, grouping several provinces and being in turn subordinated to a praetorian prefecture....

 of Thraciae

Diocese of Thrace

The Diocese of Thrace was a diocese of the later Roman Empire, incorporating the provinces of the eastern Balkan Peninsula The Diocese of Thrace was a diocese of the later Roman Empire, incorporating the provinces of the eastern Balkan Peninsula The Diocese of Thrace was a diocese of the later...

, which in turn was part of the Prefecture of the East.