passable; yet cultural relationships between Iran and India even in prehistoric times can be pointed out, and Darius the Persian controlled the Indus Valley and the Punjab for a time.
The southern border of Iran faces so abruptly on the Indian Ocean that inhabitants of this region are denied the enjoyment of maritime pursuits. North west of this district the mountain ranges which are a continuation of the Zagros chain trend with remarkable regularity from northwest to southeast. These ranges are separated by regular valleys and intersected by enormous defiles, so that passage is difficult and commerce seriously impaired.
One district alone in this region gave easy access to the plateau of Iran itself, to the Persian Gulf, and to the fertile and early civilized Babylonia. This district, the plain of Susa, geographically bade fair to be called a part of Babylonia. However, an encircling arm of the Zagros, added to the marshes which in early days surrounded the head of the Persian Gulf, protected this level basin. In the north and northeast other snow-topped ranges of the Zagros furnished abundant water for several rivers which irrigated the land. Two of these approach each other at right angles in the center of the plain. When but a few miles apart they again recede, the Karkhah turning southwest toward Babylonia, the river Diz flowing southeast into a third river, the Karun. At the point where the Karkhah and Diz most nearly ap-
