Dinís Dias and Cape Verde

Overview

Dinís Dias was a Portuguese explorer who in 1445 conducted the first of two trade missions for Prince Henry the Navigator. In the course of his first voyage he explored the west coast of Africa, which was then unknown territory, sailing past Cape Bojador and the mouth of the Sénégal River to discover Cape Verde, the westernmost point of Africa. Dias called the area the "green cape" in honor of its tall trees and abundant plants. Dias significantly increased geographic knowledge of the West Coast of Africa.

Background

Prince Henry, son of the Portuguese King John I, was a key figure in Portugal's Age of Discovery. In 1415, he assisted in leading the Portuguese army in the conquest of Ceuta, a Muslim stronghold in North Africa. There he became interested in the geography, history and precious metals trade of western Africa. Prince Henry's impressions of the continent were based on rudimentary accounts and maps made by Arab geographers, which were sketchy and often wrong. For example, early maps showed the Sénégal River originating in a lake in central Africa, and claimed that this river was the source of the Egyptian Nile. The land beyond Cape Bojador, a tiny cape south of the Canary Islands, was marked terra incognito—unknown territory.

The Arabs called it Abu Khatar, "the father of danger," and Portuguese sailors feared it greatly. They knew its coast was too shallow for navigation, and believed that the water surrounding it "boiled." Conventional wisdom said that there were no water, vegetation, or people beyond that point, and that anyone foolish enough to venture beyond the cape would be lost forever. We know now that the constant north-south flow of the Canary current along the coast made it possible for ships to sail southward to West Africa but prevented a return voyage along the same route.

Undaunted, Prince Henry began sending expeditions southward along the west coast of Africa. Between 1424 and 1434 fifteen expeditions tried unsuccessfully to round the Cape. Finally, in 1434, Gil Eannes found that by sailing westward into the open sea, then turning east, he was able to round the Cape. This successful passage effectively ended the superstitions and fueled Prince Henry's confidence in his scientific approach to navigation. His crews continued to venture farther south towards the Sénégal River and the yet-to-be-discovered Cape Verde. New navigational aids such as the compass, astrolabe, and more accurate maps contributed to the success of later voyages.

After the breakthrough voyage around Cape Bojador Portuguese expeditions were immediately sent to explore rivers and coast to the south. Rivers such as the Sénégal and Gambia were important because they were an interconnected system of protected waterways that linked the rich interior trade routes of Africa to the coast. Some of these expeditions were successful in bringing back commodities such as oils and skins, but most were used for slave raids in the early 1440s.

In 1445 Dinís Dias was commissioned by Prince Henry to lead an expedition of caravels to the west coast of Africa. He sailed southward past the delta of the Sénégal River and reached a point of land he named Cape Verde, "the green cape," after seeing the first lush vegetation in nearly 800 miles (about 1,300 km). Although Dias did not realize it at the time, Cape Verde was the westernmost point on the African continent.

Sailing further south, Dias noted that the coast began to curve eastward, inspiring false hopes that he had rounded the African continent. When the Portuguese tried to land to go ashore, they were beaten back decisively by the natives. They returned a year later in another expedition sponsored by Prince Henry to explore the Sénégal River, then considered a western branch of the Nile.

Impact

Prince Henry the Navigator was a driving force behind Portugal's Age of Discovery, the period of African coastal exploration that was to culminate with Vasco da Gama's voyage around the Cape of Good Hope and on to India. The number of works translated into Portuguese during the fifteenth century attest to Prince Henry's interest in all aspects of exploration. In 1419 he established a center for sailors, mapmakers, and other interested in navigation and discovery at Sagres, a town on the Portuguese coast.

At the school seamen were given instruction in new navigational techniques. Henry's captains were probably taught to use compasses, astrolabes, and maps. After each voyage they related all pertinent navigational and geographic information they'd acquired on the journey in order to update the charts for subsequent voyages. This system established a reservoir of useful and accurate information.

The Caravel

This kind of knowledge was necessary because sailing the open Atlantic was a different and far more difficult proposition than had ever been attempted. The Mediterranean was a long, narrow, enclosed sea where sooner or later a familiar landmark would come into view. The prevailing westerly and northwesterly winds made sailing along the coasts of Europe and Northwest Africa fairly easy. As exploration moved southward, however, reaching a specific destination meant learning about new wind patterns and ocean currents, as well as acquiring sophisticated sailing techniques and incorporating new ship designs.

Early Portuguese explorers sailed barcas and barinels, square-sailed ships that were clumsy and slow to respond. Prince Henry realized that a new type of ship and sail were needed to travel southward. Dias captained a newly designed ship known as a caravelas or caravel. This innovative design incorporated an axled rudder and three to four masts with triangular lateen sails, which gave the ship both speed and agility. The deck planks were with coated with shredded hemp and a layer of tar or pitch to improve water resistance.

This change in ship design was accompanied by improved navigation techniques. Prince Henry and other explorers had rediscovered Claudius Ptolemy's (c. 85-c. 165) Geography, a compilation of latitudes and longitudes of the known world known first published in 151 that had been translated from Greek into Latin in the early 1400s. Fifteenth-century astronomers used the Geography and other Arab works to produce almanacs showing the positions of stars and planets for each day of the year. This information became very useful in navigation during Dinís Dias's time.

The Astrolabe and Navigational Aids

Another important navigational tool was the stella maris, or astrolabe, that allowed navigators to read the height of the North Star. The quadrant, a quarter circle measuring 0° to 90° marked around its curved edge, was used to determine latitude. Its straight edges had tiny holes or sights located on each end and a plumb line hung from the top. The navigator lined up the holes and the plumb line would hang straight down over the curved area at a particular point. This would indicate the height of the stars in degrees and give the latitude. If, for example, a star measured 50° above the horizon, it meant they were at a latitude of approximately 50° north. Once mariners had gone beyond where the North Star was visible, they began to use the Southern Cross for reference.

Sailors would not be able to determine longitude until the chronometer was developed in the eighteenth century. In Dias's time sailors used an ancient technique known as "dead reckoning," to make a crude estimate of longitude by measuring the ship's speed, time, distance traveled, and direction. Dead reckoning also took observations of known landmarks, cloud formations, and wind and wave patterns into account.

In addition to better navigation, sea captains kept detailed notes of their expeditions for future use in portolanos or charts that showed bodies of water, landmasses, and ports. Compiled by masterful navigation and personal experience, these maps made the successful exploration of the coast of west Africa possible.

LESLIE HUTCHINSON