Iraq, a triangle of mountains, desert, and fertile river valley, is bounded on the east by Iran, on the north by Turkey, on the west by Syria and Jordan, and on the south by Saudi Arabia and Kuwait. It is twice the size of Idaho. The country has arid desert land west of the Euphrates, a broad central valley between the Euphrates and the Tigris, and mountains in the northeast.
From earliest times Iraq was known as Mesopotamia—the land between the rivers—for it embraces a large part of the alluvial plains of the Tigris and Euphrates rivers.
An advanced civilization existed in this area by 4000 B.C. Sometime after 2000 B.C., the land became the center of the ancient Babylonian and Assyrian empires. Mesopotamia was conquered by Cyrus the Great of Persia in 538 B.C. and by Alexander in 331 B.C. After an Arab conquest in 637–640, Baghdad became the capital of the ruling caliphate. The country was pillaged by the Mongols in 1258, and during the 16th, 17th, and 18th centuries was the object of Turkish and Persian competition.
Under the influence of the monsoons, Iraq in summer has a constant northwesterly wind (shamal), while in winter a strong southeasterly air current (sharqi) develops. The intensely hot and dry summers last from May to October, and during the hottest time of the day—often reaching 49°c (120°f) in the shade—people take refuge in underground shelters. Winters, lasting from December to March, are damp and comparatively cold, with temperatures averaging about 10°c (50°f). Spring and autumn are brief transition periods. Normally, no rain falls from the end of May to the end of September. With annual rainfall of less than 38 cm (15 in), agriculture is dependent on irrigation.