Anno Domini: The Marriage of Theophanu and Rufus

If you ask me, one of the fun questions of history involves the issue of the continuity of the western calendar. 

Specifically, by what grounds do we assert the calendar we use today, that tells us we are in the year 2020, reflects the correct number of years that have passed since Antiquity?

Or equivalently, how do we know that our Common Era is the same as the original Anno Domini that was invented by Dionysius Exiguus (who discovered he was in 525)?

How do we know 2000 years have passed since the year we now call AD 20?

Or to narrow it down a bit, how do we know that after Dionysius Exiguus did this calculation, that 447 years elapsed until the very fascinating event below?


525 -- Anno Domini, Dionysius Exiguus
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 Theophanu was escorted to Rome for her wedding by a delegation of German and Italian churchmen and nobles.  Her uncle John I Tzimiskes had overthrown his predecessor  Emperor Nikephoros II Phokas in 969.

972 Apr 14  -- Marriage of the niece of the Eastern Roman Emperor John I Tzmiskes (fourteen-year-old Theophanu [Θεοφανώ]) to co-emperor of the West and son of Western Emperor Otto I the Great (sixteen-year old  Otto II [Otto Rufus (the Red)]) in Rome, performed by Pope John XIII,. The Pope crowns Theophanu as Western Empress.

Let's assume this event is correctly dated (by year*) in our current 2020 calendar.
(1000 years before April 1972*)

*That our April 14 in 2020 may not line up exactly with the fourteenth day of the month April in 972 AD, but some other day in April perhaps, is in known feature. It happens on a small scale year by year because of leap year. But even with other calendar adjustments since the Middle Ages, this amount of offset is always by less than a month in the calendar. What we are concerned with is the number of solar years that have passed between two year-dates. 

How do we know this year-counting sequence is correct during the gap in recorded western history? 

There are no reliable continuous records in the Western or Eastern Roman Empire covering this gap. 

There are no reliable historical chroniclers during this gap. 

Anno Domini was not widely used until much later. 

How did they keep count in a reliable way? 

Who would have been able to do that?
 How can we be certain that they got it right?

Western Emperor Otto II in 985.