It’s interesting that most people seem to forget or ignore the Eastern Roman/Byzantine empire for some reason. No state contributed more to preserving ancient knowledge and Constantinople was absolutely central to that. e.g. if it had fallen to the Arabs in the the late 600’s the dark ages would have been a lot darker an possibly would have never ended (e.g. the collapse of Roman-Hellenic civilization would have been a lot more similar to the bronze age collapse.

Also the downfall of the (Eastern) Roman Empire mostly coincided with the high middle ages and early renaissance. And contact with the empire arguably was much more important for kickstarting the renaissance than that with North Africa or the middle east.