Theodosius’ legislative plans were part of a wider program that aimed at restoring order, and contrasted with barbarian disintegration and incoherence. One of the more delicate problems was the definition of the border between the two “empires” or sections (partes) of an empire aiming at reunification. In the past, the Illyrian sector—today we would call it the Balkans—was considered part of the “West,” partly because it was believed that the Danubian frontier was strategically essential for the defense of Italy. The established balance between the two parts was modified in 395, with the division of the empire and the creation of the new prefecture of Illyricum, which was added to the existing ones of the East, Gaul, and Italy-Africa. Theoretically, the jurisdiction of the Illyrian prefecture went from Greece to the Danube, but because of the ambiguity in Theodosius’ instructions, both the partes of the empire were quarrelling over the new administrative sector. Now that relations between Ravenna and Constantinople had so much improved, the favored option was to divide Illyricum, which would have important consequences for centuries to come. While Ravenna controlled the upper and mid-Adriatic, Constantinople had consolidated its grip on eastern Illyria and, of course, Greece. The border on the River Drina, which Santo Mazzarino called an “iron curtain,” separated two parts of the peninsula, which up to that time had been considered a single geographic unit and perhaps also a strategic unit, but which now led to a cultural separation even in political terms—and that ongoing separation was between the Latin-speaking regions and Greek-speaking ones.

From Giusto Traina’s 428 AD: An Ordinary Year at the End of the Roman Empire, Princeton and Oxford: Princeton University Press, 2009 (first published in 2007), pp. 44-45.