https://en.wikipedia.org/wiki/Phantom_time_conspiracy_theory
The Holy Roman Emperor Otto III conspired with Pope Sylvester II (and quite possibly the Byzantine Emperor Constantine VII as well) to doctor the dating system. The trio cooked the books to place their reigns at A.D. 1000, which they did because it is an auspicious number.
The three men added 297 years of bogus history to the early medieval period to facilitate this deception.
