Just curious, seems like something someone would make special note of at the time, at least someone looking at a calender, looking outside and saying, "Huh, it's been a thousand years since Jesus was born, that seems sigifigant."
There is always more to say, and, while this topic comes up a fair bit, we could certainly do with more comprehensive responses to the question than we've got so far – but you might like to review a couple of existing resources from AH while you are waiting for fresh responses to your query.
Was the millennium from 999-1000 ad marked in any special way?, with u/savvysioux
and
Did people in 999AD celebrate the new millennium? Were there any doomsday predictions similar to Y2K, with u/haimoofauxerre