The German economic historian Fanz Oertel in the 1950s points to another drastic consequence of a slave economy. A slave economy initially allowed an increase of productivity through the invention and use of new machinery. Roman products remained at a simple level and could be reproduced by handicraft. By the fourth century, for example, the robust pottery industry of Greece was in sharp decline because other parts of the empire also learned to make pottery.
"The decline in international trade in the Mediterranean in the fourth century was partly due to increasing piracy, but it was also due to lack of industrial innovation and of need for exchange of manufactured goods.

Autore: Norman F. Cantor