Estimating gross domestic product in ancient times

Question

I would like to estimate, to what extent the Roman republic (or different parts of it) were "agricultural".

Today, a common measure to the "agricultural-ness" of an economy is the gross domestic product in agriculture, divided by the total gross domestic product. E.g, if the GDP in agriculture is 10 billion and the total is 400 billion, then the economy is about 2.5% agricultural.

Is there a way to estimate these numbers for ancient economies such as the Roman republic?

Alternatively, is there another way to estimate the size of agriculture relative to the size of other industries?

(I am also interested in data for other ancient economies, but it seems that data for Rome is easier to find).

Answer 1

Using workers' income figures in specific sectors may be difficult, since some sectors relied a lot on slaves (e.g. mining), and others may have used different sources of manpower in different geographic regions (e.g. agriculture: free workers in Italy, slaves in Sicily). So the income aproach may be difficult.

Likewise, the expenditure approach may be complex, unless we have access to data on the consumption of goods (through the amount of taxation levied upon goods, perhaps?)

This would leave us with the production approach, i.e. determine the amount of goods produced in each geographical region, find market prices for these goods, multiply getting the production value per sector and per region.

Just an impression I have: maybe the Roman Empire is actually a good place to try this out, since a relatively small types of goods seem to have occupied a disproportionately large proportion of trade. Transport of olive oil, wine, wheat, metals (and slaves?) would cover a large part of what has been found in shipwrecks. Of course, this should not let us forget smaller production of goods not offered up for trade. Brassica in Campania would have mostly been consumed locally. But it may give a rough idea of the relative importance of productive sectors.

What I am wondering about is how to estimate the importance of the terciary sector. May not be easy when doctors, scribes, et al. will often have been slaves bought for the task.

HTH

Answer 2

For your specific problem a more direct approach might be to compute the agricultural potential given a particular set of technologies. If you can figure out how much grain a farmer could produce, then you can potentially estimate what fraction of the population had to be farmers.

There are studies of this topic. For example, "Estimating the agricultural base of Greek Sicily" byFranco De Angelis, or "Metropolis and Hinterland: The City of Rome and the Italian Economy, 200 BC-AD 200" by Neville Morley (1996) or "Farm Equipment of the Roman World" by K. D. White (2010) or "Famine and Food Supply in the Graeco-Roman World: Responses to Risk and Crisis" by Peter Garnsey (1988) etc etc.

For example, lets imagine that with Roman technology a farmer can maintain 30 acres and each acre yields 30 bushels of wheat on average. Then every year the farmer will produce 900 bushels of wheat. One bushel will yield about 40 pounds of flour or 900 x 40 = 36,000 pounds of flour, each pound making a loaf. If one person eats 1 loaf per day, then the 36,000 pounds of flour will support about 100 people. If the farmer's family and hands amount to 10 people, then 10% of the population would be farmers or members of a farming family. A crude estimate no doubt, but it may give you an idea of how to do your own analysis.