Cape Bojador, on the coast of present-day Western Sahara, was Europe's wall. Generations of mariners treated it as the non plus ultra, the point beyond which one did not go, a barrier as much in the mind as in the water. In 1434 Henry's squire Gil Eanes finally rounded it and came back alive. The following year Henry sent Eanes out again, this time with a second vessel under Baldaia's command, ordered to press on into the unknown. The two ships ran south to a bay they called Angra dos Ruivos, Bay of the Reds, named for the abundance of red fish in its waters, some 250 kilometres past Bojador, along a coast so empty they found only footprints, human and camel, and met no one at all.

In 1436 Baldaia sailed again, alone this time, ordered to bring back a living inhabitant of the coast and carrying horses aboard in case he had to chase one down on land. He never caught anyone. But pressing south he reached an inlet that fooled him completely: a deep coastal cut he took for the mouth of a great river. He named it Rio do Ouro, the River of Gold, certain he had found the fabled waterway that Saharan traders said led to the wealth of the Mali Empire. He had not. The real river of gold, the Senegal, lay far to the south, and the inlet near modern Dakhla held no treasure at all, only basking monk seals, which his crew slaughtered for their pelts and oil before sailing on.

From the false river Baldaia drove still farther, and in doing so he may have crossed a line no European had crossed before by sea: the Tropic of Cancer, an invisible boundary on the chart that nonetheless mattered enormously to men reared on warnings that the southern oceans were unsurvivable. He reached a galley-shaped rock he called Pedra da Galé, off Cape Barbas, and there found nothing but abandoned fishing nets. So he turned back, having pushed roughly 125 miles past the previous year's limit. Prince Henry, hoping for gold or captives, was disappointed by the bare report and let the whole project rest for years.

Baldaia's coast did not stay empty for long, and what followed darkens his achievement. The same waters he opened became the path for Portugal's expansion down the African coast, and within a few years that expansion turned to human cargo: the trade that would center on the slaving fort at Arguin, just up the coast from Baldaia's voyages, hauling captured Africans back to Europe. The explorer himself sailed on to a quieter end. He became a customs collector in Porto and, most likely, one of the first settlers of Terceira in the Azores, where he built a home and chapel and died in 1481. Today his figure stands carved into Lisbon's grand Monument to the Discoveries, a cup-bearer turned navigator, remembered for opening a coast whose consequences he could not have foreseen.