Commerce, at times destroyed by conquerors and at other times obstructed by monarchs, surveys the earth, flees from where it is oppressed, pauses where it is allowed to breathe ; it reigns today where once there was nothing but deserts, seas and boulders ; and where it once reigned there are only deserts.
To see Colchis today, which now is just a vast forest where the people, declining by the day, defend their liberty only to sell themselves one by one to the Turks and Persians, one would never say that this region had in Roman times been full of cities to which trade called every nation on earth. Nothing is left of them in the area ; traces are found only in Pliny  and Strabo. 
The history of trade is the history of the communication of peoples. Their various destructions, and certain ebbs and flows of populations and devastations, constitute its greatest events.