In 1874 Stanley undertook and carried through in the face of terrible difficulties one of the most remarkable and valuable journeys in the history of African exploration. He settled the question as to the relative importance of the Albert Nyanza and the Victoria Nyanza, discovered the Mwuta Nzige (Lake Albert Edward), and crossed Africa from east to west, starting from Zanzibar and travelling down the Lualaba from the point where Livingstone had left it to its mouth, thus proving it to be the upper level of the Congo. This great journey opened up the hitherto unknown country in the centre of Africa, and led directly to the formation of the Congo Free State. Stanley had been preceded at Nyangwe, the point of departure for the voyage down the Congo, by Lovett Cameron, who failed, however, to follow the river throughout its course, and reached the coast to the south of its mouth. In 1884 Joseph Thomson supplemented Stanley’s work by his journey to Mounts Kilimanjaro and Kenya through Masailand to Victoria Nyanza. Wissmann and other German explorers (1881–6) did much for a knowledge of the great southern tributaries of the Congo, while Wissmann in 1881–2 crossed the continent from west to east. It has been frequently crossed since. Stanley’s expedition up the Congo to rescue Emin Pasha (1887–89) opened up the great Central Africa forest with its pigmies, extended our knowledge of Lake Albert Edward and its outlet the Semliki, which flowed into the Albert Nyanza, and revealed the great snowy range of Ruwenzori, which was ascended and mapped by the Duke of the Abruzzi in 1906.