What exactly is "the pre-industrial average"? does that correspond to the Little Ice Age? why is that a good reference point, or baseline for comparison?
538 karma · joined July 31, 2018
Mainz was also part of Germania and is much further East.
The current extent of modern Köln is much wider than that of the Roman city of 20,000 people, so you'd have to dig in very specific places to find Roman artifacts.
My personal favorite would be to recover all of the texts by pre-Socratics.