Watered by the Jordan, Euphrates and Tigris rivers and covering some 400-500,000 sq. km. with a population of 40-50 million, the region extends from the eastern shore of the Mediterranean Sea around the north of the Syrian Desert and through the Jazirah and Mesopotamia to the Persian Gulf.
The western zone around the Jordan and upper Euphrates rivers gave rise to the first known agricultural settlements 11,000 years ago. The earliest known settlements are at Iraq ed-Dubb (Jordan) and Tell Aswad (Syria), followed shortly later by Jericho. The earliest cities, states, and writing arose later in Mesopotamia ("between the rivers", referring to the land between the lower Euphrates and Tigris) in the east.
The region's natural fertility has been greatly extended by irrigation works, upon which much of its agricultural production continues to depend. The last two millennia have seen repeated cycles of decline and recovery as past works have fallen into disrepair through the replacement of states, to be replaced under their successors. Another ongoing problem has been salination - the seepage of salt water into irrigated farmland.
As crucial as rivers were to the rise of civilization in the Fertile Crescent, they were not the only factor in the area's precocity. The Fertile Crescent possessed four of the five most important species of domesticated animals - cows, goats, sheep, and pigs - and the fifth species, the horse, lived nearby. The Fertile Crescent had a climate which encouraged the evolution of many annual plants, which produce more edible seeds than perennials, and the Fertile Crescent's dramatic variety of elevation gave rise to many species of plants for early man to experiment with.
River waters remain a potential source of friction in the region. The Jordan lies on the borders of Israel, the kingdom of Jordan and the area administered by the Palestinian Authority. Turkey and Syria each control about a quarter of the length of the Euphrates, on whose lower reaches Iraq is still more heavily dependent.