By the death of Harun in 809, Nicephorus was left free to deal with the Bulgarian king, Krum, who was harassing his northern frontiers.
Under their tsar Krum (802-815) the Bulgars invaded the districts of Adrianople and central Macedonia; under Simeon (893-927), who fixed his capital at Preslav, their empire extended from the Adriatic to the Black Sea.