 The diocese was transferred to the Western Empire in 384 by Theodosius I, probably in partial compensation to the empress Justina for his recognition of the usurpation of Magnus Maximus in the Gallic Empire.However, upon his death in 395, it reverted to the Eastern Empire, forming, together with the Diocese of Macedonia to the south, the Praetorian prefecture of Illyricum.The territory of diocese was devastated by the Huns in the middle of 5th century and finally overrun by the Avars and Slavs in late 6th and early 7th century.