In 1856 the Royal Geographical Society funded an expedition to the African Great Lakes. Burton set off from Zanzibar to explore an "inland sea" that had been described by Arab traders and slavers. His mission was to study the tribes in the area and to find out what exports might be possible from the region. It was hoped that the expedition might lead to the discovery of the source of the River Nile. Speke accompanied him and on the 27 June 1857 they set out from the east coast of Africa heading west in search of the lakes. Both men succumbed to a variety of tropical diseases on the journey, but the expedition finally reached Lake Tanganyika in February 1858.
Editors. "Richard Burton and John Speke reach Lake Tanganyika". The Literary Encyclopedia. First published 01 January 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=5010, accessed 22 February 2017.]