Thrace (Θρᾴκη) is a historic region between the Balkan Mountains, the Black Sea, the Marmara Sea, and the Aegean Sea in Southeast Europe. The name originally referred to the Thracians, an ancient people inhabiting Southeast Europe (modern in modern Bulgaria, Greece, and European Turkey). Rome annexed the Thracian kingdom, whose ruler were previously client kings of Rome, in 46 CE, after which it was made into a Roman province. Diocletian reorganized the area between the Lower Danube and the Aegean into the diocese of Thrace around 300.

The name Thrace in Late Antiquity included the provinces of Europa, Thracia, Haemimontus, Rhodope, Moesia II, and Scythia. Philippopolis (modern Plovdiv) was the capital of the province of Thracia. During this period it was attack by the Goths, Huns, and Slavs, after which the Slavs and Bulgars settled in the area. It is unclear whether Opsikion and Thrace were two themes or whether the district of Thrace was joined to neighboring Opsikion when the theme system began to emerge. By the 11th century, Thrace as an administrative unit usually appears combined with Macedonia under the command of the same strategos. While Thrace seems to have later disappeared from official administrative nomenclature, the name continued to be used by some antiquarian writers.