I think (having quickly looked at Wiki) that it might be a 19th century idea that a certain medieval time in England could reasonably be called 'the dark ages'. But certainly, as a child, the kids history books I had and loved, tended to call the some medieval times that, with a view that the Renaissance ended it. I don't think now this is right, but it does seem that at some point in the past some historians did think this way. Have not read Pryor so cannot comment on how fair he was to other historians.

The Silk Roads book is full of migrations of one sort or another. And cross-cultural knowledge and scholarship. The trade routes themselves, the author argues where places where ideas and religion travelled, so presumably stories too.