In 400 AD Rome hosted a population of well over a million people, 200 years later the population of the city was counted in low tens of thousands. So, was there just a gigantic empty ghost town located in the center of Italy? What happened to all that infrastructure?

by Ikkon

So I was thinking today: Between 100 BC and 400 AD Rome was a home to well over a million people, at times even nearing 1.5 million according to some sources. Even by modern standards it was not a small city. But having so many people required a lot of dense urban housing and a robust infrastructure. Hundreds of thousands of different structures, packed densely in the center of the metropolis.

Then in 500 AD the population fell to just around 100 thousand people, and then even more to just some 50-30 thousand people over the entire medieval period. At times it was supposedly completely abandoned.

So, was something like 90-95% of the city just completely empty for few hundred years? Was there a gigantic post-apocalyptic urban wasteland, full of empty houses, in the heart of Italy? Or were they all destroyed when the city started shrinking?

kirino_imouto

Not only in Rome, but the urban population of the regions of the Roman Empire also declined everywhere (more in the Western half than in the Eastern half). This collapse of the urban population followed long-run patterns of economic change.

Historians like Ian Morris, Josiah Ober, Alain Bresson, Walter Scheidel, and Ward Perkins are good references regarding long-term economic waves in Western Eurasia. There were three big waves:

Bronze Age Civilizations flourished until the late 2nd millennium BC, they collapsed during the Early Iron Age, also called Greek Dark Ages, and it took centuries for civilization to flourish again with the same intensity,
Developing from 9th century BC to peaking in terms of economic complexity/social development around the peak of Roman Empire in the 1st and 2nd centuries AD. Then declining and collapsing in late-antiquity and the early middle ages (from 150 AD to 750 AD).
Our modern civilization which began its cycle of flourishing with the medieval efflorescence in the 10th to the 14th centuries and continued to the present. We still have not had a large decline in the economic complexity of our civilization. Although we had recessions lasting a few years like The Great Depression and The Great Recession, our civilization appears to not have reached its peak in economic complexity yet.

This book is a good summary of Morris' research:

https://press.princeton.edu/books/hardcover/9780691155685/the-measure-of-civilization

This book by Ward Perkins is a good one explaining in detail the collapse of economic activity in the Western half of the Roman Empire:

https://www.amazon.com/Fall-Rome-End-Civilization/dp/0192807285

This lecture video by Ward Perkins gives a summary of the book:

https://youtu.be/__HoBL_RD9w

So, the decline in the urban population in the city of Rome was not quick, Rome's population likely peaked at over 1 million around 100 to 150 AD, before the Antonine Plague. Then it slowly declined over the centuries. By the early 5th century it was already substantially smaller than during its peak.

Since houses tended to degrade the city did not look "empty" instead, tons of old Roman ruins were spread around mostly open plains. For example, the arena of the colosseum became grassland for sheep and according to this illustrated map, even around early modern period 16-17th centuries, Rome was still contained in a small fraction of the Aurelian Walls, built in the late 3rd century:

http://www.vidiani.com/maps/maps_of_europe/maps_of_vatican/detailed_antique_map_of_rome_city.jpg

Note the numerous ruins dating from the Roman period.

The_Bunglenator

This answer from u/bitparity may help:

https://www.reddit.com/r/AskHistorians/comments/1m5gfc/what_was_the_city_of_rome_like_in_the_dark_ages/cc69g1o?utm_medium=android_app&utm_source=share&context=3