Was this really the greatest hoax ever perpetrated, or was there real substance to these letters?
Some scholars claim the letters were forgeries made by Nestorian Christians and Cochin Jews from Malabar in India.
How easy would it have been to fool Popes and emperors at that time? One has to think that no simple ruse could have worked. Even in those times, leaders had sufficient resources at their disposal to verify claims of these types. Merchants, travelers and spies did manage to make their way to the East and certainly would have been consulted for independent confirmation.
After the Mongol invasions, three main theories regarding Prester John arose in Europe as travelers began bringing back tales from faraway places. These were the original one of Prester John of the Indies, an Ethiopian version and a Central Asian one.
Marco Polo and Friar Odoric were among those who claimed that Prester John was a Central Asian Kereit khan who had adopted the Nestorian religion. Jordanus was the first to claim that the kingdom lie in Ethiopia.
In the 15th century, an emissary of the Negus of Ethiopia proclaimed that the emperor was Prester John motivating the navigators of Portugal to explore Africa. In the following century though, we again hear of letters from Prester John of the Indies, some written in the Hebrew language.
The book Igeret Orhot Olam, written by Abraham Farissol in the early 16th century claimed that Prester John's kingdom lied somewhere "beyond Kalicut" a port in South India.
If you remember, Malabar was the beginning of India Major, one the three "Indias" according to medieval European geographers. It was to here that the Portuguese explorers came on their way to the East Indies, establishing the colony of Goa located in the present-day state of Kerala.
Europeans eventually found the islands of spices and the gold islands that they had heard about, but never quite resolved the mystery of Prester John. Maybe part of the problem is that the closer they came to the actual kingdom, the smaller and more isolated the latter became. By the time full-fledged expeditions had reached the actual location, the ancient empire for the most part had vanished, and only legends existed.
Even up to the time preceding Magellan's 16th century voyage, tales of a mysterious kingdom in the Indies persisted. Mendes Pinto, writing about a decade earlier, tells of the kingdom of the Lequios, the Liu-Kiu of the Chinese, located between the coast of China and Mindanao to the south. He gives a latitude of 9N20 for this kingdom and strongly suggests that the kings of Europe make an expedition there.
When Magellan neared the Philippines he had set his course a bit further north at 13N heading for "Gaticara" according to Pigafetta and Albo.
The Chinese Liu-Kiu was probably the same location described by the Japanese as Mishima "Three Islands." It included Taiwan, Luzon and another island of unsure location. The neighboring region was called Pi-she-yet by the Chinese, which may be a corruption of Bisaya, the central Philippines region.
Duarte Barbosa wrote of the Lequios/Liu-Kiu:
From Malaca they take the same goods as the Chins [Chinese] take. These islands are called Lequios. The Malaca people say they are better men, and richer and more eminent merchants than the Chins. Of these folk we as yet know but little, as they have not yet come to Malaca since it has been under the King our Lord.
Barbosa thought the Lequios were inhabited by "white men" who resembled Europeans, a belief possibly generated by the medieval romances.
I would suggest that the letters of Prester John were part of an overall campaign by the empire of Sanfotsi/Zabag to arrest intrusions on its trade routes. Not that Prester John penned these himself, as the letters suggest he had others in his service including westerners who could have composed them with his instruction.
Starting as early as the late 10th century, Sanfotsi began requesting assistance from the Sung emperors against their neighbors and competitors to the south. At the same time, they began strenghtening their relations with kingdoms in eastern India and Tibet. These kingdoms were on the edge of the Islamic expansion. They may have hoped here not only to gain allies but to strengthen the resolve of the nations to resist the Muslim juggernaut.
The Tibetans knew of the Shambhala king and his great palace where nearby was located a "park called Malaya where sandalwood trees grow...with the scent of camphor, which seems, so one feels, to remove all the sufferings of existence."
About a century after the Kalacakra Tantra, with its battle machine recommendations, reaches Tibet, we begin to hear of eastern contacts with the Christian world. These culminate in the famous letters of Prester John in the middle of the 12th century.
But as time rolls on the priest-king loses much of his hand, and he must resort to bluffing more and more as the empire decreases. Although the letters took a life of their own, it's difficult not to see historical reality behind them.
Paul Kekai Manansala
Bar-Ilan, Meir, Prester John: Fiction and History, http://faculty.biu.ac.il/~barilm/presjohn.html
Bernbaum, Edwin, The Way to Shambhala, Boston: Shambhala Publications Inc., 2001.