The old unified Sudan was the largest country in Africa with a total area of 2.5 million km². It is bounded on the east by the Red Sea and is surrounded on the other sides by nine African nations. Its terrain is characteristically flat, except for a few mountain areas, including the Imatong–Didinga range in the south, the Red Sea Hills in the east and Jebel Marra in West Darfur. The most salient geographical feature is the River Nile basin that traverses the country from south to north. The River Nile is composed of two main branches – the White Nile that originates in the Equatorial Lakes and the Blue Nile that descends from the Ethiopian Highlands. The two rivers unite in Khartoum to form the River Nile that runs to the Mediterranean Sea. The river Nile and the mountains constitute special sites, characterised by high rains and waters of special importance to Sudan.