>The income is of course lower, however.

Yes, but perhaps not as much as one might expect. Relevant Reddit post:

TIL that the Roman Empire in the year 150 was so wealthy that all of Western Europe may not have equaled its GDP until 1500 (<https://np.reddit.com/r/todayilearned/comments/3prsxr/til_th...>)

I was hoping someone would take this data and calculate an approximate Big Mac index. I big difference is the price of poultry vs beef, perhaps indicative of the industrialisation potential of poultry farming vs beef farming that has since been realised.