What city was Charlemagne crowned emperor of?

Answer 1

Charlemagne was not crowned emperor of a city. He was crowned Emperor of the Romans, implying that he was ruler of the Roman Empire.

There was, and still is, much controversy over this event. We do know know what the intent was or even who was behind it. Charlemagne is said to have taken the position that the coronation was a surprise to him, but many people have found that hard to believe. The Byzantine government, which still called itself the Roman Empire, took issue at the whole thing, as can well be imagined.