The theme of Thessalonica (Greek θέμα Θεσσαλονίκης ) was a Byzantine theme to the southern Balkans, the parts of the central and western Macedonia included. Its capital was Thessalonica, the second city of the Byzantine Empire.
In late antiquity, Thessalonica was the seat of the Roman province of Macedonia and the Diocese of Macedonia, also the seat of the praetorian prefect of Illyricum. With the loss of large parts of the Balkans to the Slavs in the 7th century, the territory of the prefect ( Greek Eparchos, " eparch " ) of the city and its immediate vicinity was limited. The Eparch ruled Thessalonica to the early 9th century, when he was ousted by a strategos at the top of the new theme of Thessalonica.
The strategos of Thessalonica was first mentioned in 836, but a letter of Michael III. (reigned 820-829 ) to the Frankish king Louis the Pious (reigned 814-840 ) suggests an existence of the issue already at 824. The topic was probably 809 during the campaigns of the Emperor Nicephorus I (reigned 802-811 ) established against the Slavs. To the east the topic to the river Strymon and the same topic covered. In the south, it bordered somewhere in Thessaly on the theme of Hellas. The western and southern border was constantly changing with the tide of battle against the Byzantines, the Slavs and Bulgarians.
Under Emperor John I Tzimiskes (reigned 969-976 ) was stationed in the city, who possessed professional tagmatische troops Doux. He existed for a while in parallel with the strategos of the theme, then the office of strategos was abolished. In the 11th century the Doukaton of Thessalonica was of such importance that it was often held by members of the imperial family. The city and a large part of Macedonia were conquered by the Latins after the Fourth Crusade, after which the Kingdom of Thessaloniki was founded, which in turn was conquered in 1224 by the Despotate of Epirus. After the city and Macedonia were in 1246 fell to the Empire of Nicaea, the subject was recovered and survived until the city was conquered by the Ottomans in 1392. Byzantium regained the city in 1402 and a Despotat was established here until the city was given up voluntarily in 1423 in Venice. 1430 the Ottomans conquered the city again.