Key Points

• The Dark Ages didn't exist, it was a creation of a Holy Roman Emperor
• This is due to miscalculated corrections in the Gregorian calendar.
• Evidence and history were made up by the Roman emperors and 'the powers that be' for centuries afterwards and (this is the dull one) from misinterpreted archaeological evidence 
• It is believed that counting tree rings and carbon dating are faulty and don't accurately measure time.
• Another proof is the lack of architectural and cultural advance in this period.
• Astronomical observations, that were supposedly fabricated are scientifically correct for what we see today

Either the best lie in (potentially false) history, or a really (really) extravagant conspiracy theory...