In 1838 it became the route of the Delaware and Raritan Canal, and more recently of the Pennsylvania Railroad between New York and Philadelphia.[3] The early Aryans, in their gradual dispersion over northwestern India, reached the Arabian Sea chiefly by a route running southward from the Indus-Ganges divide, between the eastern border of the Rajputana Desert and the western foot of the Aravalli Hills.

The streams flowing down from this range across the thirsty plains unite to form the Luni River, which draws a dead-line to the advance of the desert.

Here a smooth and well-watered path brought the early Aryans of India to a fertile coast along the Gulf of Cambay.[4] In the palmy days of the Mongol Empire during the seventeenth century, and doubtless much earlier, it became an established trade route between the sea and the rich cities of the upper Ganges.[5] Recently it determined the line of the Rajputana Railroad from the Gulf of Cambay to Delhi.[6] Barygaza, the ancient seaboard terminus of this route, appears in Pliny's time as the most famous emporium of western India, the resort of Greek and Arab merchants.[7] It reappears later in history with its name metamorphosed to Baroche or Broach, where in 1616 the British established a factory for trade,[8] but is finally superseded, under Portuguese and English rule, by nearby Surat.

Thus natural conditions fix the channels in which the stream of humanity most easily moves, determine within certain limits the direction of its flow, the velocity and volume of its current.

Every new flood tends to fit itself approximately into the old banks, seeks first these lines of least resistance, and only when it finds them blocked or pre-empted does it turn to more difficult paths.
[Sidenote: Regions of historical similarity.] Geographical environment, through the persistence of its influence, acquires peculiar significance.