Encouraged by their example, Antonio Gonzales, and Nuno Tristram, in 1441, sailed as far as Cape Blanco, "a feat," says Faria y Souza "that is generally looked upon as being little short of the labours of Hercules," and they brought back with them to Lisbon some gold-dust taken from the Rio del Ouro. In a second voyage Tristram noticed some of the Cape de Verd Islands, and went as far south as Sierra Leone. In the course of this expedition, he bought from some Moors off the coast of Guinea, ten negroes, whom he took back with him to Lisbon and parted with for a very high price, they having excited great curiosity. This was the origin of the slave-trade in Europe, which for the next 400 years robbed Africa of so many of her people, and was a disgrace to humanity. In 1441, Cada Mosto doubled Cape Verd, and explored a part of the coast below it. About 1446, the Portuguese, advancing further into the open sea than their predecessors, came upon the group of the Azores. From this time all fear vanished, for the formidable line had been passed, beyond which the air was said to scorch like fire; expeditions succeeded each other without intermission, and each brought home accounts of newly-discovered regions. It seemed as if the African continent was really endless, for the further they advanced towards the south, the further the cape they sought appeared to recede. Some little time before this King John II. had added the title of Seigneur of Guinea to his other titles, and to the discovery of Congo had been added that of some stars in the southern hemisphere hitherto unknown, when Diogo Cam, in three successive voyages, went further south than any preceding navigator, and bore away from Diaz the honour of being the discoverer of the southern point of the African continent. This cape is called Cape Cross, and here he raised a monument called a padrao or padron in memory of his discovery, which is still standing. On his way back, he visited the King of Congo in his capital, and took back with him an ambassador and numerous suite of natives, who were all baptized, and taught the elements of the Christian religion, which they were to propagate on their return to Congo.