How did Charlemagne preserve Roman culture and civilization in wetern Europe?

Answer 1

+ Yes he did the above but more fundamentally he kept a major portion of what used to be part of Rome under a single rule for his lifetime and a little beyond, defining the shape of part what we know today as Western Europe. By doing this he handed down some of Rome's heritage a little longer and implanted it just a little deeper.

Answer 2

He put a Roman veneer on his rule by calling himself the Holy Roman Emperor. He did encourage education and the use of Latin as the official language.