My grammar book states that we use Perfect Continuous to make an emphasis on the duration of the action, that is why that tense usually goes with words like how long, since and for.
However, there are 2 sentences with a slight difference.
I have been studying English for 5 years (I started doing it in the past and continue to do it)
I have studied English for 5 years (I started doing it in the past but I may have already finished doing it or I want to say that I have kind of experience in learning the language)
That is almost clear to me, but I can't understand why it is correct to use Perfect tense here
Over the centuries, the river has played a very important role in the history of Russia.
Doesn't over the centuries imply the length of the action?
Could you, please, help me with this confusion?