For two centuries

Question

Hello, is there some connotation needed for this to trigger the Preterite? Like "These two centuries out of the 5000 years we're talking about"? Or at least "These two very specific centuries"? As opposed to "For two full centuries, which is pretty much forever", where I would have expected the Imperfect.

Answer

Hola Torsten
To use the Preterite with the time phrase "durante dos siglos" we would have to convey that something happened during two specific centuries seeing this period of time as something with an end, for example:

Durante ocho siglos, los musulmanes, los cristianos y los judíos convivieron en el territorio español en armonía. 
For eight centuries, muslims, christians and jews lived together in the Spanish territory in harmony.

So, in the speaker's mind, this is seen as something that happened within that period of time and had an end. We see it as a completed action.
We could also use the Imperfect here, although less common, in which case we would be referring to this coexistence as something that "was happening" during that period of time, without giving any relevance to when it ended. It'd be more descriptive of what was happening during that time.
Here is a lesson that talks about those specific nuances with the Indefinido (preterite) and the Imperfect. Have a look here. 
I hope it clarifies it.
Saludos