The Arabs had great wealth : they dereived it from their seas and their forests ; and as they purchased little and sold much, they attracted to themselves the gold and silver of their neighbors. Augustus learned of their opulence, and resolved they should be his friends or his enemies.  He sent Elius Gallus from Egypt to Arabia. He found people who were idle, tranquil, and unseasoned. He delivered battles, set sieges, and lost only seven soldiers ; but the perfidy of his guides, the marches, the climate, hunger, thirst, diseases, and ill-taken measures cost him his army.
He therefore had to be content with trading with the Arabs as other peoples had done, in other words, bringing them gold and silver for their commodities. We still trade with them in the same way : the caravan from Alep and the royal vessel from Suez carry immense sums there. 
Nature had destined the Arabs for trade ; she had not destined them for war ; but when these tranquil peoples found themselves on the borders of the Parthians and Romans, they became auxiliaries of both. Elius Gallius had found them to be traders ; Mohammed found them to be warriors : he gave them some enthusiasm, and made conquerors of them.