The grim letter described the imminent arrival of an alignment of the planets that would spell doom in the sky. The writings were oddly detailed about God's plan: Although the cataclysm would cause drought, famine, earthquakes, and disease all over the place, the areas most affected by divine destruction would be cities like Mecca and Baghdad, and scores of Muslims would convert to Christianity in desperation.
Now, when we say the letter was bullshit, we don't just mean the apocalypse stuff (if you're not familiar with the time period, we should note here that the apocalypse did not in fact occur). Although it may really have been sent from the university at Toledo, it was written under a fake name, following a pre-existing template that proved so popular that similar letters would appear throughout the Middle Ages. It was a lazy hoax by some random asshole.
it was basically the 4chan copypasta of the 12th Century.
Too bad the priests and noblemen weren't in on the joke.
The Third Crusade.
The letter's message that God would finally step in to take non-Christians to task resonated heavily throughout Europe, which suddenly remembered it still had an ax to grind with the Muslims after the unmitigated disaster that had been Crusade 2: The Crusadening. As such, many notables clung to the letter's messages, and it ended up being one of the deciding factors that whipped up European nobility enough to have another crack at reclaiming Jerusalem. What could go wrong?