During the 1440s, Nuño Tristão explored a large portion of Africa's west coast in a series of expeditions commissioned by Portugal's Prince Henry the Navigator. Tristão, one of Prince Henry's most trusted sea captains, is credited with the discovery of Cape Blanc, Arguin Island, and the Gambia River. Tristão was one of the first Europeans to engage in the slave trade, and under his command Arguin Island became the staging area for slaves bound for Portugal. This fertile period of exploration of Africa's western coast established Portugal as a leader in the emerging colonial world.
In 1415 Portugal began its era of geographic discovery and the establishment of colonies. At the time it had a relatively stable monarchy whose kings encouraged maritime trade. Portugal's natural geographic position on the Iberian Peninsula encouraged exploration in Africa. In 1415 the reigning royal family of John I took part in the assault on the port of Ceuta in northern Morocco. Ceuta, highly prized, was the terminus of the trans-Sahara trade route. After the successful invasion of Ceuta, the small, unrecognized country of Portugal began the domination of Europe over Africa and Asia that was to last for the next 400 years.
The riddle of the unknown Atlantic had fascinated many generations of seamen. By the middle of the fourteenth century many cartographers felt that there was a sea route to India; however, the official doctrine of the Church was based on the mappa-mundi, the wheel map that put Jerusalem in the center of the inhabited world with the continents placed around it.
Before Prince Henry, no one had attempted to venture out to the Sea of Obscurity or the Ocean of Darkness, as it was called, because of existing superstitions and frightening myths. According to accounts, monsters swam in the seas, and the overhead sun made the seawater boil and melted the pitch holding the ship's wooden beams together. The people inhabiting the African shore were known to be burned black by the sun and there was fear of being roasted alive. Magnetic rocks encouraged compasses to fail and if a ship escaped these hazards, it was only a matter of time before they would be caught in the steady flow of water that poured night and day over the edge of the flat world. Today it is known that the constant north-south flow or the Canary Current along the Saharan coast made it possible for ships to sail southward as far as West Africa but prevented a return voyage. Cape Bojador, south of the Canary Islands represented the point of no return.
The coast of Africa was only known as far as Cape Nao, because of rumors that those who ventured beyond it would never return. In 1419 or 1420, less than five years after the fall of Ceuta, a Portuguese expedition under the command of João Gonçalves Zarco rediscovered the island of Madeira. In 1427 and 1432, two expeditions succeeded in reaching the Azore Islands where large quantities of timber were used for shipbuilding. For nearly twelve years Prince Henry sent out fourteen expeditions with the aim of rounding Cape Bojador, on the coast of what is know the Western Sahara. In 1432, Gil Eannes successfully rounded Cape Bojador.
In 1441,Prince Henry outfitted two of the new caravel ships for separate journeys down the west coast of Africa with the instructions to travel south and capture native people for interrogation. Nuño Tristão, one of Henry's most trusted and experienced captains was given command of one ship and Antão Gonçalves the other. The two ships met at Rio de Oro in Western Sahara. They came across a market run by black Muslims dressed in robes and turbans. Although they had instructions to approach the local people peaceably, a skirmish ensued and ten prisoners were taken. Gonçalves sailed back to Portugal with the captives. Tristão continued an additional 320 miles south and named it Cape Blanc for its white sand.
In 1442, Prince Henry sent Nuño Tristão on another expedition. On this voyage he traveled past Cape Blanc and below Cape Anna and discovered the Arguin archipelago. This discovery played an important role in Portuguese history, for it was here on the main island that Prince Henry authorized a fort and trading post that marked the beginning of colonialism in Africa. In addition, Tristão captured fourteen natives on Arguin Island and returned to Portugal a hero. The island became a busy slave-trading station, and for the next few years, Tristão made a series of slave raids on the coast of West Africa.
In 1446, Tristão set out on his third and last voyage. Instructed by Prince Henry to push southward, he sailed beyond the Sénégal River, passed Cape Verde, the westernmost point in Africa, and sailed beyond the mouth of the Gambia River to an unnamed river. They launched the ship's boats and traveled upstream, where they were met by a barrage of poisoned arrow, hurled by hostile natives. Only five crew members survived the attack. The bodies of Nuño Tristão and eighteen of his men were buried at sea.
The Portuguese navigations during Prince Henry's influence opened a new and unprecedented chapter in human history. Prince Henry combined his political and organizational talents to catalyze the great era of Portuguese exploration and discovery of which Nuño Tristão was a part. Prince Henry established himself at Sagres and although he never went to sea, he was influential in guiding the direction of Portuguese exploration for generations to come. He set in motion a program emphasizing geographical exploration, instead of focusing on commercial voyaging. He surrounded himself with scientists, geographers, astronomers and cartographers that led to the design of the caravel, the compilation of sea charts and sailing rudders and improved methods of navigation.
Nuño Tristão was entrusted with sailing the first caravel, when he succeeded in reaching Cape Blanco in 1441. Twelve years of experimentation went into the evolution of this innovative design. The difficulty ships experienced when returning to Portugal against the prevailing north winds led to the evolution of the caravel. A hybrid, the ship's hull was modeled on the Atlantic fishing boat and the mast structure was borrowed from ships used in the Mediterranean. With its triangular sails, and small crews of thirty or less, the caravel was well adapted to maneuvering in and out of estuaries and shoals along the western coast of Africa.
The success of Portuguese navigation depended, in great measure, on the work of Prince Henry and the captains he inspired and supported. The sailing conditions in the southern Atlantic were considerably different than navigating the familiar waters and landmarks in the Mediterranean and the northern European coast. Rarely out of site of land, European sailors had reasonably accurate charts of the main landforms and they mainly traveled in north to south directions. However, when Prince Henry's ships began exploring the south Atlantic they had no charts or familiar landmarks. Expert cartographers and astronomers assisted Prince Henry in correlating information brought by returning sea captains and detailed charts and maps slowly became more accurate and useful.
The navigator's tools were the compass, sun and stars, and the astrolabe. The astrolabe was an efficient instrument for obtaining a position by sun or star altitudes. Portuguese navigators used the compass, a small magnetized metal bar mounted over cards with wind roses painted on them. With these tools, the captains and crew would note the changing altitudes at various points along the route. As new capes, headlands, and bays were discovered, they were fixed for latitude and added to Prince Henry's master chart. Gradually the men became familiar with deep-sea voyaging, and as the tools of the trade became more sophisticated, the voyages became more routine. The boiling ocean, the flood of waters at the world's end, and the magnetic rocks that destroyed ships were forgotten as the scientific approach to navigation took hold.
As for Tristão's slave raids, they continued until 1445, when Prince Henry refused to allow his crews to kidnap Africans. Prince Henry, like many Europeans, saw Africans as potential Christian converts, and when first slaves came to Portugal, they were permitted to intermarry with the Christian Portuguese and absorbed into society. They were also permitted to buy their freedom. Prince Henry's dictum against abducting slaves, however, did little to stop the lucrative trade in human beings, which continued for the next 300 years.
In the fifteenth century, it must be remembered, the idea of slavery was not a new one. It was as old as civilization itself, appearing in ancient Egypt, Greece, and Rome. In addition, slavery was a recognized hazard for every European seaman who sailed the Mediterranean, since Moorish pirates sought both human and inanimate cargo. Men who were taken prisoner during warfare knew that they would probably become slaves. In addition, slavery had always been an integral part of African culture and society, and black slaves had been traded to the Islamic world since the middle of the seventh century.
The widespread nature of slavery made it an easy and profitable business for the Portuguese. Beginning about 1450, Portuguese merchants bought slaves from the northward-bound caravans from Arguim, tapping into a longstanding trans-Saharan trade. By the end of the fifteenth century, 1,200-2,500 slaves per year were being exported. This complex preexisting system contributed to the massive exportation of Africans during the next two centuries.