In the history of the Portuguese Age of Discoveries, the focus has been on the maritime exploits of the day, with Bartolomeu Dias sailing round the Cape of Good Hope at the southern tip of Africa in 1488, paving the way for Vasco da Gama's historic crossing of the Indian Ocean to arrive at Calicut on 20 May 1498.
Historians still marvel at the speed at which the Portuguese spread their presence in Asia, especially given that they merely found themselves joining a web of well-established trade routes criss-crossing the Indian Ocean (and later the South China Sea). In fact, a little-known detail helps explain this.
John II of Portugal (Dom João II) was crowned King in 1481 and rather brutally set about consolidating his power. Along with reinvigorating the Portuguese economy, John II also revived the work of his great-uncle, Prince Henry the Navigator (Infante Dom Henrique). Under his reign, the exploration of the Atlantic made great progress, with the explicit goal of finding a maritime route to India and breaking the Muslim stranglehold on the spice trade.
Hungry for geographical knowledge, D. João II had extracted much information from Berber, Arab and Persian merchants. The little-known detail that enabled the Portuguese to rapidly set themselves up in the Indian Ocean after 1498 was his decision more than a decade before that to send merchant-spies to gather firsthand knowledge of what lay to the east and south of the known Muslim territories.
Pêro (sometimes written as Pedro) was born in Covilhã, in the Beira Interior of Portugal, not far from the Spanish border. (It so happens that this inland city produced many notable contributors to the Portuguese Discoveries.) An adept swordsman, he worked as a young man in Castile and mastered both Castilian Spanish and Arabic. Back in Portugal, he served D. João II's father King Afonso V as a squire. D. João II realized Covilhã's talents and sent him on secret missions to both Spain and Morocco.
In 1487, D. João II sent Covilhã and the ill-fated Afonso de Paiva on a mission of exploration to what is today's Middle East, as well as adjacent areas of both Africa and Asia. The two assignments were first to learn as much as possible about the sources of spices, and second to find an overland route to the legendary land of Prester John, the king of a lost Christian nation that had been cut off from Europe by Muslim and pagan lands.
Covilhã and Paiva set off from Santarém and their travels by land and sea took them together to Barcelona, Naples, Rhodes, Alexandria and Cairo, disguised as honey merchants. They joined a caravan across the Sinai Desert to reach the Red Sea, and then sailed to Aden. There, Paiva headed for Ethiopia and was never heard from again, while Covilhã made his way across the Indian Ocean on a dhow and reached Calicut. By 1488, he was already in Goa, 10 years before Vasco da Gama showed up in India with his fleet.
Covilhã then turned back westward to Hormuz, which straddles the Gulfs of Oman and Persia. A hub of the Indian Ocean trade at the time, Hormuz was an excellent place for reconnaissance and Covilhã collected and recorded detailed information about sailing routes, winds, currents, ports and politics. He didn't stop there and continued as far south as today's Mozambique, scouting for information. Less than a decade later, Vasco da Gama relied on an experienced pilot enlisted at the (now Kenyan) port of Malindi to cross the ocean to India, and some historians believe this was helped by intelligence collected by Covilhã.
Returning to Cairo in 1491, Covilhã met messengers from D. João II – two Jewish Portuguese, one a rabbi and the other a shoemaker. Covilhã passed on all the intelligence he'd gathered and then attempted one more mission before the final order to return to Lisbon, which was to find out more about the legendary King Prester John. Via the Arabian peninsula, Covilhã made it to Abyssinia and was received by the Christian Emperor Eskender. This (partially) solved the mystery of Prester John as Europe finally made contact with the Ethiopians, who had become Christian even before the Roman Empire officially converted in 380 AD under Emperor Theodosius I.
Unfortunately for Covilhã, he proved too valuable to Eskender and his successors. He was granted "lands and lordships" in Ethiopia, continued to correspond with D. João II and his successor D. Manuel I, and even received priests and an ambassador sent from Lisbon. However he was never allowed to leave and he died in Ethiopia after spending more than 40 years away from Portugal.