The Balkan Mountains run through the center of Bulgaria. They are the longest mountain range in Bulgaria and divide the country into northern and southern regions.
The Stara planina mountain (Стара планина)
Balkan mountain range
Varna
Its the Danube river and Danube plain separates Romania and Bulgaria. There are no mountaneous border between the mentioned two countries. And Carpathian mountain range of Romnia or Balkan mountain range (most northern mountains of Bulgaria: none of them serves as border.
The Balkan Mountain range (in Bulgaria Balkan Mountain is often called the 'Stara Planina' Mountains)
Stara Planina
Balkan mountain range, The Daniube and a capital Sofia!
There are two mountain ranges extended beyond the frontier of Bulgaria.a. The Balkan Mountain Range (local name- Stara Planina), extended deep in Serbia. Its in the northern half of Bulgaria. Direction: North West proceedingb. The Rhodopes Mountain Range (local name- Rodopi), passed inside Greece. Its in the Southern half of Bulgaria. Direction: South East proceeding
the Jura mountain range is in eastern France, on the border with Switzerland. The mountain range in south central France is called 'le massif central'
Tilarán mountain range
A common mountain range covering Bulgaria and Serbia is called the Balkan Mountains (in Bulgarian also called 'Stara Planina')