Dealing in Arabia Felix and in the Indies were the two branches, and almost the only ones, of foreign trade. The Arabs were then what they are today, equally devoted to dealing and to banditry. Their vast deserts on the one hand, and the riches they went to seek there, produced these two effects. They found these riches in their seas and in their forests ; and as they sold much and purchased little, they attracted to themselves the Romans’ gold and silver.  We still trade with them in the same manner : the caravan from Aleppo and the royal vessel from Suez bear immense sums there. 
Their trade with the Indies was considerable. Strabo had learned in Egypt that they employed one hundred twenty ships for it  ; this trade still maintained itself only with their silver. Every year they sent fifty million sesterctii. Pliny says that the merchandise they brought back sold in Rome for a hundred times that.  I think he speaks too generally : such profit made once, everyone would have wanted to do it ; and from that moment no one would have.
One can doubt whether it was advantageous to the Romans to carry on trade with Arabia and the Indies. They had to send their silver, and they did not have, as we do, the resource of America which makes up for what we send. I am persuaded that one of the things that made them raise the face value of moneys, which is to say to establish alloyed coinage, was the rarity of silver caused by its continual shipment to the Indies. Now if the merchandise coming back sold in Rome for a hundred times more, the Romans’ profit was made off the Romans themselves, and did not enrich the empire.
It might be alleged, on the other hand, that this commerce procured a great deal of shipping, in other words great might, for the Romans ; that the new kinds of merchandise increased domestic trade, favored the arts, and supported production ; that the number of citizens multiplied in proportion to the new means of livelihood ; that this new commerce produced the luxury which I have shown to be as favorable to the government of one man alone as fatal to the government of many ; that this establishment occurred at the same time as the fall of their republic ; that luxury was a necessity in Rome ; and that a city which drew in all the wealth in the world had to give it back through its luxury.
 I will say only a word about domestic trade.  Its principal branch was that of grains that were imported for the subsistence of the people of Rome, which was a policy matter rather than an object of commerce. For this purpose the navigators received some privileges,  because the salvation of the empire depended on their vigilance.