THE COUNTRIES BOUNDING the Persian Gulf include Oman, United Arab Emirates, Qatar (a peninsula off the Saudi Arabia coast), Bahrain (an island), Saudi Arabia, Kuwait, Iraq, and in the north, Iran. The Persian Gulf is an arm of the Arabian Sea extending some 600 mile (970 kilometer) from east to west. It covers an area of approximately 89,000 square mile (230,000 square kilometer) and the greatest depth is 335 foot (102 meter). It is connected to the Arabian Sea in the east by the Strait of Hormuz. Its southern coastal area is characterized by low desert plains. The western coast continues as desert plains with a coastal escarpment that leads into a major river delta known as the Shatt al-Arab. The northern coast is more rugged but equally desert. The ancient Greeks named the gulf as “Persian” and so it has appeared in sources from antiquity and is in common use until today. Some Arab states and authors sponsor a modern revision to the “Arab Gulf.” The Persian Gulf has acted as a route for trade since the earliest millennia of human civilization. From 4000 Before Common Era onward, increasing complex trading relationships are supported by archaeological evidence. Trading centers such as Dilham (most likely modern Bahrain) and Madgan (Oman) linked Mesopotamia to the Indus Valley in South Asia. As the dynasties of history grew greater, the more elaborate the trade links. Intervening cities and ports flourished as suppliers and middlemen along this flow of metals, wood, spices, incense, and finished goods. The Persian Gulf proved to be perfect for this gradual growth of trade and enabling technologies. The simplest boats could move down these feeding rivers to the salty shores of the gulf and sea and make their way along coastlines to their partners in trade and commerce. The domestication of camels led to the expansion of land routes of commerce that enhanced the Persian Gulf trade. Shipbuilding technologies improved and the discovery of the monsoons for seasonal travel to and from India modified routes and trade links. A Persian Gulf coast culture based upon cities of commerce developed and prospered. The settled people of the Persian Gulf coast differed from the nomadic peoples of the interior of the Arabian Peninsula and the lands along the northern coast of the gulf. The nomads were children of the deserts, and the coastal peoples were dependent upon the sea. One moved across endless deserts to points of water that gave life to their flocks. The other settled on the shores of the endless waters to capture the largess that made their livelihood. If the deserts could not feed their flocks, the nomadic tribes pushed into the settled towns of agriculture and trade. Cycles of tribal incursion onto the coastal settlements blended Arab culture with that from Mesopotamia and the lands of India, continuing to build a unique Persian Gulf character. Also, these settlements and the tribes that plied the Persian Gulf began to take on an increasingly Arab flavor because of the consistent out migration from the Arab interior. Some Arab tribes from the rocky wastes and scattered oases of the peninsula came to the coasts and adopted the less mobile life of the settlement. Other tribesmen, masters of the sand, became masters of the sea. They took up sailing and began to build the legend of Arab traders and pirates. In 325 Before Common Era, Alexander the Great sent fleets of ships from India to explore the shores and islands of the Persian Gulf. Greek influence was not able to take permanent hold; by 250 Before Common Era the Parthians had brought the gulf under predominantly Persian control for the first time. This control of the Persian Gulf from a northern empire would last until the coming of ISLAM. Islam spread to the gulf during the life of the Prophet Muhammad and soon reached to all peoples on its shores. The prosperity of the Persian Gulf continued as in 750 C.E. Baghdad became the seat of the caliph and the main center of Islamic civilization and power. Oman was positioned geographically to take advantage of sea routes in the Persian Gulf and to the Red Sea. The lands around the mouth of the Persian Gulf became the stronghold of those seeking to challenge the powers that controlled the Persian Gulf trade from along the Tigris and Euphrates. Thus began a dance of influence in the Persian Gulf as powers in Mesopotamia vied with those in Muscat. This foretold the long history of conflict between those in the Persian Gulf against outside powers who sought to control this strategic body of water because of the wealth it could command. By the year 1000, Persian Gulf merchants were traveling regularly to Southeast Asia and beyond to China. Their trading efforts were instrumental in spreading Islam, first to India and then to Indonesia and Malaysia. The tribes of the interior remained culturally distinct from the gulf coastal peoples even under Islam. Empires based in Persian and Iraq depended on customs duties from the East-West trade in the Gulf. Those Arabs along the coasts always had to deal with these external factors. This reality led to political compromises and some cultural concessions. Those in the interior often remained more conservative and traditional. The coastal cities and accompanying wealth of trade passed through the hands of many Islamic rulers over the years be they from Mesopotamia, Persia, or Arabia.