Several mountainous areas define the landscape, most notably the Stara Planina (Balkan) and Rodopi mountain ranges, as well as the Rila range, which includes the highest peak in the Balkan region, Musala. In contrast, the Danubian plain in the north and the Upper Thracian Plain in the south represent Bulgaria's lowest and most fertile regions. The 378-km (235 mi) Black Sea coastline covers the entire eastern bound of the country. Bulgaria's capital city and largest settlement is Sofia, with a permanent population of 878,000 people.