Of the Bantu tribes along the seaboard north of the Umzimvubu a good deal of knowledge was obtained during the sixteenth century by the crews of wrecked ships, some of whom underwent almost incredible suffering before their restoration to the society of civilised men. By order of King Sebastião a flying survey of the coast between the Cape of Good Hope and Cape Correntes was also made during the years 1575 and 1576, by which much information was supposed to have been gained.

Occasionally vessels disappeared after leaving Portugal or India, and were never heard of again. Some of these were probably lost on the African shore, though of this there is no certainty except in one instance, when part of a stranded ship was found at the mouth of the river now known as the Saint Lucia, but without a trace of any one that had sailed in her. Particulars, however, have been preserved of the loss successively of the São João, the São Bento, the Santiago, the São Thomé, and the Santo Alberto, from each of which some of the crew escaped, and after much intercourse with Bantu succeeded in reaching Mozambique.

The São João was a great galleon laden with a very valuable cargo, which left Cochin on the 3rd of February 1552 to return to Portugal. She had about two hundred and twenty Portuguese and nearly four hundred slaves on board, and, as was usual at that time, an officer of high rank who was going home was captain in command.