Basic Introduction (story background for anyone interested)
I have a character whose punishment for causing massive genocide was immortality for ten thousand years. To be more specific, after his death, his soul was imprisoned in a special container for ten thousand years. After his punishment, he sees the world once again and is surprised that technology hasn't developed much.
So, the question is, how could have civilizations not have had any significant technological change? How could they have been stuck in medieval technology?
I'm asking this question because I'm planning to write about what happened in the past (ten thousand years ago) and what happens in the present (basically the protagonists trying to defeat the returned villain). I want them to both have medieval settings, as I did lots of research on a medieval setting, and I don't want the characters of the ten-thousand-years-before plot to be unorganized, primitive people.
The setting is fantasy, so the explanation can be magic-related.
The technology of ten thousand years before and later are both medieval technologies (6th~7th century).
"Civilizations" in this question refers to all the civilizations living on one big continent. Also, it doesn't have to be only one country that has been standing for ten thousand years; multiple countries must have fallen and have been established over the course of ten thousand years.
No external forces impeding technology; there is no big force trying to prevent technological development.
No major technological developments as in no society-changing inventions (guns, steam engines) were made.
Religion: There could be multiple religions that developed, or just one unifying one.
The continent these civilizations are living in is half the size of Africa.
If technology staying stagnate isn't possible at all, a fall and then a rise would be okay.
The introduction is only an introduction. You don't have to worry about it when answering the question.