Professor Dutton (YouTube) claims there are some techniques that indirectly offer insights.
Easiest is to study numbers of new ideas, inventions , patents, tech improvements etc. When a civilization’s people become dull these all drop in rate per population unit.
Got a link to the Roman patent office?
‘Easiest is to study numbers of new ideas, inventions , patents, tech improvements etc. When a civilization’s people become dull these all drop in rate per population unit.”
Unfortunately, the Rome patent office was temporarily closed 9am17pm, 1AD to 1850AD.