The point is, both of these men knew how to self-mythologize, which is why Heribert Illig, a German systems analyst, believes that the two changed the date in order to make their ascent to power even more symbolic. It's possible that the two came to power at the middle, or end, of the seventh century AD, and simply rewrote the dates to make it look like they were on the brink of a new millennium.
Illig has a few interesting pieces of evidence to support him. There are allegations of widespread document fraud in several manuscripts written at the time, which seem to date from the seventh century. Byzantine documents from this era were transcribed from one kind of script to a new, more efficient script, and the originals were thrown away. Perhaps they were thrown away to conceal gaps and inconsistencies in the historical record.
Did A Pope And An Emperor Team Up To Erase 300 Years Of History?
The change-over from the Julian to the Gregorian calendar in 1582 was precipitated because all celebrations were about 10 days off from when they "should" be, seasonally-speaking. The gap of 10 days was far too short for a calendar system that had been accruing errors for 1500 years. Ten days only accounts for about 1200 years — leaving 300 years unaccounted for.
(...) It's worth noting that most historians vehemently disagree with this interpretation of events. Although the medieval period was turbulent, and most of the population did not have a good sense of the date, quietly adding 300 years to the timeline would have been too much of a stretch, even for the two most powerful and motivated men in Europe. That being said, it's an incredible idea, that two people invented three centuries, bending time to their will. And it makes our civilization quite advanced, considering we're living in the 1700s.