From time to time the world puts itself into situations that change commerce. Today the commerce of Europe is principally carried on from north to south. At this time the difference of climates causes the peoples to have great need of each other’s products. For example, beverages shipped from south to north make up a kind of trade that was unknown to the Ancients. Thus the capacity of seagoing vessels, which once was measured by quantities of grain, is now measured in barrels of liquids.
The ancient commerce that we know about, taking place between one Mediterranean port and another, was almost all in the south. Now, peoples of the same climate, having more or less the same things at home, have less need of trade amongst themselves than with those of a different climate. Trade in Europe was therefore formerly less extensive than it is today.
This does not contradict what I have said about our trade in the Indies : excessive difference of climate makes their relative needs nonexistent.