Bulgaria maintained extensive lines of fortresses to protect the country, with the capital Tarnovo in the centre. To the north were lines along both banks of the Danube river. To the south were three lines; the first along the Balkan mountains, the second along Vitosha, northern Rhodope mountains and Sakar mountain, the third along the valley of the river Arda. To the west, a line ran along the valley of the river South Morava.