In Clarke, D. (1987). Trade and Industry in Barbarian Europe till Roman Times. In E. Miller, C. Postan, & M. Postan (Eds.), The Cambridge Economic History of Europe from the Decline of the Roman Empire (The Cambridge Economic History of Europe, pp. 1-70). Cambridge: Cambridge University Press. doi:10.1017/CHOL9780521087094.003 wealth is generated by what factor of production? In other words which factor of production is the most important in making an area or region comparatively wealthy pre Rome?