In West Africa, long-distance trade across the sands of the Sahara made possible the exchange of commodities from the Mediterranean world for those of Africa, which encouraged the expansion of states south of the desert. In East Africa, long-distance trade over the waters of the Indian Ocean made possible the exchange of commodities from Asia for those of Africa, which cultivated the rise of commercial emporiums and city-states to promote them. There are striking similarities between Saharan and Indian Oceanic commerce. Both traversed great distances. The Bilma Trail (Garamantean Road) was the shortest route, 1,500 miles across the Sahara. The trade routes of the Indian Ocean were longer, thousands of miles of open water between the coast of East Africa to southern Arabia, the Persian Gulf, and the Indian subcontinent. Along these two great passages of economic, cultural, political, and religious intercourse the merchandise for trade in the great market towns were much the same – gold, ivory, perfumes, exotic woods, and slaves from East Africa in return for cloth, porcelain, salt, and hardware from Asia. There were accepted standards of exchange, tariffs, and a royal monopoly on special items such as gold and slaves and commercial agreements between rulers and merchants to promote their own and mutual interests.