Jacques de Vitry's Letter from Acre (Letter Two)
In his letter, he writes of the "Prester John Christians" of the east as likely allies in the fight against Islam. Specifically Jacques refers to a figure called King David— either the son or grandson of Prester John— a figure who was himself "commonly called Prester John." This is perhaps the first moment of Prester John as a title observed within the legend's lore.
Brewer edits and translates the letter (pp. 98-100):
But now in the city of Acre, I... await the arrival of pilgrims with great longing. Indeed, I believe that if we had 4,000 men of arms, through God's favour we would not be able to find anyone strong enough to resist us. Indeed, there is a great discord amongst the Saracens, and many of them, knowing their error for certain, if they dared to and had the help of Christians, they would be converted to the Lord. I also believe that the Christians living amongst the Saracens are greater in number than the Saracens [themselves]. Also, many Christian kings living in the Easter regions up to the land of Prester John, hearing of the arrival of the crusaders, would come to their help and go to war with the Saracens.
Later in the letter, Jacques explains that these "Prester John Christians" are Jacobites, or monophysites, an interesting contrast to the general trend of identify Prester John's people as Nestorians, who practice a dyophysite belief about Christ.
A few years later, Jacques expands on this faith by integrating the figure of King David, borrowed from a report called the Relatio de Davide that Jacques assimilated into the framework of the Prester John legend, as demonstrated in this so-called "Letter VII."
