Ethiopia is a land of rugged mountains, broad savannahs, and many lakes and rivers. The country is composed of an elevated central plateau generally varying in height from 2,000m and 3,000m. In the north and center of the country, there are up to 25 mountains whose peaks rise over 4,000m, the tallest being Ras Dejen (which means Head Guard), known as Ras Dashen, which is 4,543m in elevation. The most famous Ethiopian river is the Blue Nile (Abay), which runs a course of 1,450km from its source at Lake Tana, to join the White Nile in Khartoum