Thessalonica - A Brief History of the Byzantine Empire

Thessalonica had become Galerius's regional capital before that during the period of the Tetraki. It was ideally positioned to control the Balkans, being at the crossroads of Greece and the north but also Italy. To the east was the prefecture of Thrace, which as you can see was less mountainous and therefore a more prosperous place. In the mountains of the area, Latin remained widely spoken, but along the plain Greek now predominated.