Our urge to trade has profoundly affected the trajectory of the human species. Simply by allowing nations to concentrate on producing those things that their geographic, climatic, and intellectual endowments best enable them to do, and to exchange those goods for what is best produced elsewhere, trade has directly propelled our global prosperity.

For most of the period following the fall of Rome, the adherents of a powerful new monotheistic religion dominated medieval long distance commerce as completely as the West dominates such commerce today; the legacy of that former dominance is still all too visible.

The incense trade catalyzed the birth of Islam, whose military, spiritual, and commercial impacts transformed medieval Asia, Europe, and Africa. Riding on a rising tide of global trade along the land and sea routes of Asia, Islam came to dominate that continent's spiritual as well as its commercial life.

The coming of the Prophet would sweep away this fragmented and pluralistic pattern of trade in the ancient world. Within a few centuries of Muhammad's death, one culture, one religion, and one law would unify the commerce of the Old World's three continents nearly a millennium before the arrival of the first European ships in the East.

Although the modern image of the imperial city is dominated by the ruins of the Coliseum and the Forum, the economic life of ancient Rome centered on side streets filled with apartments, shops, and horrea.

The Stoic philosopher and playwright Seneca is said to have owned five hundred tripod tables with ivory legs—no small irony, since he was a vocal critic of the empire's extravagances.

The ancient incense trade was thus no different from the modern cocaine and heroin trades: relatively safe around the raw agricultural source, but highly risky around the finished product and its ultimate consumers.

The Umayyad and Abbasid empires were in effect large free-trade areas in which old borders and barriers had been swept away, especially along the Euphrates River, since remotest antiquity the traditional frontier between the East and West. No longer were the three great routes to Asia—the Red Sea, the Persian Gulf, and the Silk Road— competing alternatives; rather, they were an integrated global logistic system available to all parties who recognized the suzerainty of the caliphate.

Although the Anatolians and the people of the Indus Valley knew each other's products, it is not known whether or not they met each other face-to-face; rather, they would have been separated by an unknown number of middlemen.