The Origins of the Germanic-Speaking World

Genetic evidence points to mass migration in this period. The male lineages present today have more in common with the North Sea coast of the continent than they do with western Britain. So how big did a migration have to be for it to be mass migration? Thousands, tens of thousands, hundreds of thousands of people? I think tens of thousands would be enough to qualify. A few thousand migrants per year doesn't sound like many in the context of a region with a couple of million inhabitants but over a century or so, that's a huge number.