of its sources. But at this period no maps were able to give any detailed outline of the course of the river, and the tracings reproduced on the globes endeavoured to harmonise the definite statements of the Portuguese explorers with the African legends and classical traditions of Ptolemy. Thus João de Barros holds as certain that the Zaire flows from the largest lake in Africa, which is itself "the mysterious head of the Nile;" and Duarte Lopez also assigns the same origin to both rivers. Even in the maps of the eighteenth century the same false ideas hold their ground,
although Mercator had already in 1541 regularly limited the two fluvial basins by their water-partings.
The era of scientific exploration in the Upper Congo basin begins towards the close of the last century with the expedition of José de Lacerda e Almeida, who in 1798 penetrated from Mosambique to the region of the great lakes. In 1806 a more fortunate expedition was made by some pombeiros, or caravansmen, right across the continent from the Atlantic to the Indian Ocean. But of the route followed little is known beyond the fact, that, after passing the great Kwango affluent, they traversed the southern slope of the Congo basin as far as Lacerda's surveys in the
