Diocese of Macedonia

The Diocese of Macedonia (; ) was a diocese of the later Roman Empire, forming part of the praetorian prefecture of Illyricum. Its administrative centre was Thessaloniki.
History.
The diocese was formed, probably under Constantine I (r. 306–337), from the division of the Diocletianic Diocese of Moesia. It included the provinces of Macedonia Prima, Macedonia Salutaris, Thessalia, Epirus vetus, Epirus nova, Achaea, and Crete. Alongside Dacia and, until 379, Pannonia, it made up the Prefecture of Illyricum. In 379, Pannonia was detached and merged into the Praetorian prefecture of Italy and Thessaloniki became the Prefecture's new capital city instead of Sirmium.