I always think of the symbolic end of Rome as 660. Constans II comes over from Constantinople. He visits Rome which after all is still part of his empire. He walks around marveling at the glories done centuries ago. Rome has only about 50k people at this point, just the Papal bureaucracy really. It isn’t even the capital of Byzantine Italy. That’s Ravenna.

He orders his men to strip all the remaining precious metal gilding from the monuments. He even takes all the copper.

Then no Roman Emperor returns until the 15th century, unless you count Charlemagne and tue HRE.

They didn’t so much let taxation slip as they inherited a system of taxes in kind. The money economy was going away. It becomes much harder to rebuild a needed aqueduct for a city 500 miles away when you can’t pay the workers from the surplus you’ve got elsewhere. All you can do are smaller projects using your local surpluses.

I always remember that, yes Rome itself was outside the empire for 60 years after 476, but then it was back in and stayed in until about 750. Then in 800 the Pope looked around and said, “yep it’s back again” and crowned Charlemagne “Emperor.”

So the idea took forever to die.