As the modern Iran now suffers from the perpetual incursions of Uzbegs and Turcomans, so the north-eastern provinces of the ancient Persia were exposed to the raids of the Asiatic Scythians and the Massagetse, who were confined by no such barrier as the Caucasus, having merely to cross a river, probably often fordable during the summer, in order to be in Persia.

Hyrcania and Parthia had indeed a certain amount of protection from the Kharesmian Desert; but the upper valleys of the great streams--the satrapies of Sogdiana and Bactria--must have suffered considerable annoyance from such attacks.
On the side of India, the Empire enjoyed a twofold security.

From the shores of the Indian Ocean in the vicinity of the Runn of Cutch to the 31st parallel of north latitude--a distance of above 600 miles--there extends a desert, from one to two hundred miles across, which effectually shuts off the valley of the Indus from the rest of Hindustan.

It is only along the skirts of the mountains, by Lahore, Umritsir, and Loodiana, that the march of armies is possible--by this line alone can the Punjabis threaten Central India, or the inhabitants of Central India attack the Punjab.

Hence in this quarter there was but a very narrow tract to guard; and the task of defence was still further lightened by the political condition of the people.