Read a history that spans times ancient and modern, as I've been doing lately, and you encounter a striking shift in the late Middle Ages. Until that point, documentary information is scarce, and narratives must be pieced together from smatterings of written matter and archaeological evidence. Afterward, historians face a growing surfeit of information, and their challenge becomes deciding what to pay attention to.
The rise of the printing press, which Johannes Gutenberg kicked off around 1440, is the most obvious reason for the shift. Also important is the spread of literacy and literary production (aided by the invention of spectacles) that began a few centuries before Gutenberg built his press.
Nowadays, we produce information by the exabyte-load. As Google's Eric Schmidt said again and again in 2010: