Two qualities define the Nile as the ultimate river. First, it is the world’s longest river. From the source in Rwanda to the end at the Mediterranean Sea, it travels 6650 kilometres (4130 miles). Second, the Nile is a truly cosmopolitan water. Its source lies in tropical Africa, its most important tributary – the Blue Nile – originates in the Ethiopian highlands. Its longest stage – through Sudan and Egypt – is characterised by Arab influences. Travelling through a sea of sand, this river gives life. It passes Africa’s largest city – Cairo – and ends only a few hundred kilometres away from Europe, in the Mediterranean Sea.