A thousand years ago was summer in January? Since the earths axis moves, does the timing of the seasons move as well? Jesus was said to be born in the summer, do they celebrate his birthday in December for a reason?
Since the earths axis moves, does the timing of the seasons move as well?
You may get answers here, particularly from anthropologists, but do x-post this part to /r/AskScience (Astronomy category) for the math.
As for Christmas landing in December, you can get started on these posts