The Printing Press (1440)

Gutenberg's movable type printing press made books affordable to the middle class for the first time, enabling mass literacy, the rapid spread of the Protestant Reformation, the Scientific Revolution, and ultimately the Enlightenment. Before printing, ideas spread at the speed of a person walking; after it, ideas spread at the speed of a wagon. The printing press is frequently cited by historians as the single most transformative invention in the last millennium.