8. – Bulgaria at the time of Pressiam and Boris.

The rapid enlargement of the Bulgarian Empire began under Pressiam (836-553) who, profiting from the wars of the Byzantine Emperor Theophiles against the Arabs, got very easily possession of the whole Macedonia of today as far as the Servian territory on the Ibar river and as far as Albania. To the south the Bulgarian frontier enclosed the regions of Kostur, Bitolia (Monastir), Moglen, Tikwesch and Strumitza up to the west Rhodopies. The union of all these territories to Bulgaria was officially recognised by the Byzantine government for the first time in the treaty of 864, concluded with the successor of Pressiam, Boris I (853-888) one year before the conversion of the Bulgarians to Christianity (865). This agreement determined more precisely the southern frontier of Bulgaria to which was also left the stretch of land along the middle and upper courses of the rivers Struma and Mesta.

The map shows the boundary of Bulgaria according to the treaty of 864.