While authorized for three centuries, slave trade was officially condemned by several European countries by the Treaty of Vienna in 1815.

Nevertheless, it continued for half a century in spite of legal prohibitions, harsh sanctions and a strict control. 

In order to counter this control, the Negro traders adapted their ships, which became faster. The ships were fitted with layer sails and were lightered to enable them to navigate upstream the African rivers, which offered more discrete anchorage than coastal ports.