Archaeological evidence suggests that Dilmun returned to prosperity after the Assyrian Empire stabilized the TigrisEuphrates area at the end of the second millennium B.C. A powerful ruler in Mesopotamia meant a prosperous gulf, and Ashurbanipal, the Assyrian king who ruled in the seventh century B.C., was particularly strong. He extended Assyrian influence as far as Egypt and controlled an empire that stretched from North Africa to the Persian Gulf. The Egyptians, however, regained control of their country about a half-century after they lost it.

A series of other conquests of varying lengths followed. In 325 B.C., Alexander the Great sent a fleet from India to follow the eastern, or Persian, coast of the gulf up to the mouth of the Tigris and Euphrates rivers and sent other ships to explore the Arab side of the waterway. The temporary Greek presence in the area increased Western interest in the gulf during the next two centuries. Alexander's successors, however, did not control the area long enough to make the gulf a part of the Greek world. By about 250 B.C., the Greeks lost all territory east of Syria to the Parthians, a Persian dynasty in the East. The Parthians brought the gulf under Persian control and extended their influence as far as Oman.

The Parthian conquests demarcated the distinction between the Greek world of the Mediterranean Sea and the Persian Empire in the East. The Greeks, and the Romans after them, depended on the Red Sea route, whereas the Parthians depended on the Persian Gulf route. Because they needed to keep the merchants who plied those routes under their control, the Parthians established garrisons as far south as Oman.

In the third century A.D., the Sassanians, another Persian dynasty, succeeded the Parthians and held the area until the rise of Islam four centuries later. Under Sassanian rule, Persian control over the gulf reached its height. Oman was no longer a threat, and the Sassanians were strong enough to establish agricultural colonies and to engage some of the nomadic tribes in the interior as a border guard to protect their western flank from the Romans.

This agricultural and military contact gave people in the gulf greater exposure to Persian culture, as reflected in certain irrigation techniques still used in Oman. The gulf continued to be a crossroads, however, and its people learned about Persian beliefs, such as Zoroastrianism, as well as about Semitic and Mediterranean ideas.

Judaism and Christianity arrived in the gulf from a number of directions: from Jewish and Christian tribes in the Arabian desert; from Ethiopian Christians to the south; and from Mesopotamia, where Jewish and Christian communities flourished under Sassanian rule. Whereas Zoroastrianism seems to have been confined to Persian colonists, Christianity and Judaism were adopted by some Arabs. The popularity of these religions paled, however, when compared with the enthusiasm with which the Arabs greeted Islam.

Data as of January 1993