Pannonia and western Illyria, or Dalmatia, were assigned to the prefecture of Italy, Thrace to that of the Orient, while the whole centre of the peninsula, from the Danube to the Peloponnese, constituted the prefecture of Illyria, with Thessalonica as capital.

To avoid the merited vengeance of many individuals whom he had ill-treated, he was obliged, on giving up his prefecture, to make a precipitate retreat from Clermont.

The dividing line followed that, already mentioned, which separated the prefecture of Italy from those of Illyria and the Orient, that is to say, it began in the south, on the shore of the Adriatic near the Bocche di Cattaro, and went due north along the valley of the Drina till the confluence of that river with the Save.