Humans actually knew the earth was round as early as 2500 years ago. Eratosthenes calculated the circumference of the planet to an astounding accuracy of around 99%.
A monk had once written over a book that contained information about calculus in ancient Greece that could have made us 100 or even 1000 years more mathematically and technologically advanced.
A German mathematician spent a decade writing a 200 page manuscript about drawing a regular 65537 sided polygon with a compass and a straightedge.
Hypatia, the first well known woman mathematician, was murdered by a mob of Christians who ripped off her skin with sharp tiles and seashells.