Prince Henry's plan requires the circumnavigation of Africa.

His early voyages stay close to the African coast.

After repeated attempts, Gil Eanes finally rounds Cape Bojador on the west coast of Africa in present-day Western Sahara in 1434, a psychological, as well as physical, barrier that is thought to be the outer boundary of the knowable world.

After passing Cape Bojador, the exploration of the coast southward proceeds very rapidly.

In 1436 Gil Eanes and Afonso Baldaia arrived at the Senegal River, which they call the River of Gold because two Africans they had captured are ransomed with gold dust.

In 1443 Nuno Tristão arrives at the Bay of Arguin off the coast of present-day Mauritania.

These voyages return enslaved Africans to Portugal, which sparks an interest in the commercial value of the explorations, and a factory is established at Arguin as an entrepôt for human cargo.

In 1444 Dinis Dias discovers the Cape Verde Islands, at this time heavily forested, and Nuno Tristão explorea the mouth of the Senegal River.

In 1445 Cape Verde is rounded, and in 1456 Portuguese arrive at the coast of present-day Guinea.

The following year, they reach present-day Sierra Leone.

Thus, when Prince Henry dies in 1460, the Portuguese have explored the coast of Africa down to Sierra Leone and discovered the archipelagoes of Madeira, the Azores, and the Cape Verde Islands.

Nuno Tristão, a knight of the household of Henry the Navigator, is in 1441 dispatched by Henry in one of the first prototypes of the lateen-rigged caravel to explore the West African coast beyond Cape Barbas, the furthest point reached by Gonçalves in 1436).

Around Rio de Oro, Tristão met up with the ship of Antão Gonçalves, who had been sent on a separate mission by Henry that same year to hunt monk seals that basked on those shores.

But Gonçalves happened to capture a solitary young camel-driver, the first native encountered by the Portuguese since the expeditions began in the 1420s.

Nuno Tristão, who carried on board one of Henry's Moorish servants to act as an interpreter, interrogated Gonçalves's captive camel-driver.

Tristão and Gonçalves were led by his information to a small Sanhaja Berber fishing camp nearby.

The Portuguese attack the fishermen, taking some ten captives, the first African slaves taken by the Portuguese back to Europe.

Gonçalves returns to Portugal immediately after the slave raid, but Nuno Tristão continues south, reaching as far as Cape Blanc (Cabo Branco), before turning back.

Nuno Tristão is in 1443 sent out by Henry again, and presses beyond Cape Blanc to reach the Bay of Arguin.

On Arguin island, Tristão encounters a Sanhaja Berber village, the first permanent settlement seen by Henry's captains on the West African coast.

Tristão immediately attacks it, taking some fourteen villagers captive and returns to Portugal with his captives.

Portuguese explorers will sail the coast of Africa throughout the fifteenth century, establishing trading posts for several common types of tradable commodities at the time, ranging from gold to slaves, as they look for a route to India and its spices, which are coveted in Europe.

A new ship, the small, highly maneuverable caravel, allows Portuguese seamen to sail to Senegal.

The lateen sails give her speed and the capacity for sailing to windward (beating).

The Portuguese prince Prince Henry the Navigator has placed at the disposal of his captains the vast resources of the Order of Christ, of which he is the head, and the best information and most accurate instruments and maps that could be obtained.

He seeks to effect a meeting with the half-fabulous Christian Empire of "Prester John" by way of the "Western Nile" (the Sénégal River), and, in alliance with that potentate, to crush the Turks and liberate the Holy Land.

(The concept of an ocean route to India appears to have originated after his death.)

On land, he had again defeated the Moors in their attempt to retake Ceuta in 1418; but in an expedition to Tangier, undertaken in 1437 by King Edward (1433–1438), the Portuguese army had been defeated, and could only escape destruction by surrendering as a hostage Prince Ferdinand, the king's youngest brother.

Ferdinand, known as "the Constant", from the fortitude with which he endured captivity, had died unransomed in 1443.

By sea, Henry's captains had continued their exploration of Africa and the Atlantic Ocean.

In 1433, Cape Bojador had been rounded; in 1434 the first consignment of slaves had been brought to Lisbon; and slave trading had soon become the most profitable branch of Portuguese commerce, and will remain so until India is reached.

Dinis Dias had soon come across the Senegal River and rounded the peninsula of Cap-Vert in 1444.

By this stage, the explorers had passed the southern boundary of the desert, and from now on, Henry has one of his wishes fulfilled: the Portuguese have circumvented the Muslim land-based trade routes across the western Sahara Desert.

The naval expeditions that Henry had been sending down the West African coast since at least the early 1430s had, during their first few years, yielded little profit, sailing mostly along the Sahara desert coast, with no native settlements in sight or encounters worth reporting.

But in 1443, one of Henry's captains, Nuno Tristão, had returned from an expedition with some fourteen captive African natives, Sanhaja Berbers seized from small native fishing settlements he had found in the Bay of Arguin, on the Atlantic shore of Mauritania.

The prospect of easy and profitable slave-raiding grounds around the Arguin banks has aroused the interest of numerous Portuguese merchants and adventurers.

The regent prince Peter of Coimbra had in 1443 granted his brother Henry the Navigator an exclusive monopoly on all trade south of Cape Bojador.

A consortium of merchants of Lagos, sometimes referred to as the Companhia de Lagos ('Lagos Company', although it was probably little more than a temporary association of merchants, rather than an incorporated company in the proper sense), have applied to Henry for a license.

Sometime in the 1430s or early 1440s, Henry had appointed one Lançarote de Freitas (better known simply as Lançarote de Lagos), trained as a squire and chamberlain in his household, as almoxarife (customs-collector) of Lagos.

Possibly on account of his intimate relationship with Henry, the Lagos merchants elect Lançarote as their head.

Having acquired their license, the Lagos company have equipped a fleet of six ships and about thirty men that had set out for the Arguin banks in the Spring of 1444.

Lançarote's fleet heads straight to the southern end of the Arguin Bay, where they had been told by Nuno Tristão's captives that populous fishing settlements could be found.

A pre-dawn raid on Nar (Nair island) yields the first set of captives.

This is followed up by raids on the larger neighboring island of Tider (Tidra island) and Cerina (Serenni peninsula).

In just a few days, the Lagos fleet takes captive some two hundred and thirty-five hapless Berber natives.

The remaining population having fled the coastal settlements and hidden in the hinterlands, there is little point remaining in the area.

By August, the fleet has arrived back in Lagos with their human cargo.

The spectacle of the disembarkation, partition and sale of the Arguin slaves in Lagos, in the presence of Prince Henry, mounted on his horse, is described in heartbreaking detail in Zurara's Crónica.

For this lucrative enterprise, Lançarote is knighted by Henry on the spot (even though, according to Zurara, Henry gave away his own allotment —some forty-six slaves, to which he was entitled as licenser of the expedition—among his captains and household servants).

As many as forty vessels have sailed from Lagos on Henry's behalf from 1444 to 1446, and the first private mercantile expeditions have begun.

Slaves and gold begin arriving in Portugal.

Nuno Tristão, Henry's favorite captain, set out on his fourth trip down the West African coast in 1446 (or perhaps 1445 or 1447, date uncertain), searching for the source of gold and other valuable commodities that have slowly been trickling up into Europe via land routes for the preceding half century.

Somewhere south of Cap Vert, Tristão comes across the mouth of a large river.

Tristão takes twenty-two sailors with him on a launch upriver, to search for a settlement to raid, but the launch is ambushed by thirteen native canoes with some eighty armed men.

Quickly surrounded, Nuno Tristão, along with most of his crew, is killed on the spot by poisoned arrows (two might have escaped).

The death of Nuno Tristão is the beginning of the end of this wave of Henry's expeditions.

Another set of ships will still go out the next year, but will also take significant casualties, and as a result, Portuguese expeditions will be temporarily suspended.

Henry will not dispatch another expedition to the West African coast again for several years.

Tristão's report of easy and profitable slave-raiding grounds in the Arguin banks prompt numerous Portuguese merchants and adventurers to apply to Henry for a slave-trading license.

Between 1444 and 1446 several dozen Portuguese ships have set out for slave raids around Arguin Bay.

…they anchor at Tider and take an additional fifty-nine captives, before returning to Lagos.

The remaining two ships (Lourenço Dias and Gomes Pires) make their way back to Portugal by themselves (Pires making a brief stop in Cape Blanc, to buy some seal pelts and slaves from some Berber traders).

Little more is heard about Lançarote de Lagos.

In number of captives, the 1445/6 slaving expedition had been somewhat of a disappointment (at least relative to the first 1444 expedition).

The prospect for future slave raids seems dim.

The Arguin banks are devastated and it is unlikely the Berber populations will return to the coasts in significant numbers, or allow themselves to be taken by surprise.

The Wolof-dominated coasts of Senegal are too strong and alert for small groups of venturing Portuguese slave-raiders.

If slave raids are to have any prospect of success, the element of surprise is necessary, which now means sailing well below Senegal to new 'hunting grounds' - lengthier expeditions which require probably more supplies and capital than what Lagos merchants are willing to front or captains willing to sail.

The killing of Nuno Tristão and his crew the next year (1446 or 1447) probably dampens any remaining enthusiasm among Lagos merchants for renewing the slave raids.