You're thinking on too small a scale. One of the most important commercial activities in the Roman Empire was the importation of grain from across the Mediterra

You're thinking on too small a scale. One of the most important commercial activities in the Roman Empire was the importation of grain from across the Mediterranean (especially from Egypt) to the capital. https://en.wikipedia.org/wiki/Cura_Annonae https://en.wikipedia.org/wiki/Cura_Annonae