Searching libraries doesn't sound very revolutionary, but finding Cicero's letter, he initiated the Renaissance and helped pull Europe out if the Middle Ages.
Searching old monastic libraries, Francesco Petrarca (1304 - 1374) found personal letters from the Roman philosopher and statesman Cicero. Reading his beautiful Latin, he discovered the Latin language has degraded over time. Shocked by this, he termed the period after the fall of Rome the Dark Ages. Leonardo Bruni (1370 - 1444) was confident enough to claim they had entered a new era of rebirth, or Renaissance.
"The Great World History Book"