When the western Roman empire collapsed in 476 AD, very few people in the streets of Rome would have noticed for some time. The aqueducts still worked. The forum was still a forum. The emperor of the east, in Constantinople, still claimed dominion over the entire Roman world, and continued to claim it for another thousand years. The fall of Rome, in other words, was a process the participants barely lived through.
This is the strange thing about empires. They never end on the day the textbooks say they end. They linger, in the buildings and the laws and the languages and the half-conscious assumptions of the people who lived inside them. The British empire formally dissolved in stages between 1947 and 1997, and yet you can still hear its grammar in the way English is spoken on six continents.
The question this essay is interested in is not when an empire ends, but what of it survives. Empires are remarkably durable systems, and their afterlives (the institutions, vocabularies, road networks, and biases they leave behind) often shape the world far longer than the empires themselves did.