It was not only to the west of the Caspian that the danger threatened.  East of that sea also was a vast steppe-region—­rolling plains of sand or grass—­the home of nomadic hordes similar in character to those who drank the waters of the Don and Wolga.  The Sacse, Massagetse, and Dahse of this country, who dwelt about the Caspian, the Aral, and the Lower Jaxartes, were an enemy scarcely less formidable than the Sarmatians and the Scyths of the West.  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.  The Gangetic Indians, though brave and powerful, were politically weak, from their separation into a number of distinct states under petty Rajahs, who could never hope to contend successfully against the forces of a mighty Empire.  Persia, consequently, was safe upon this side, in the division of her adversaries.  Nor had she neglected the further security which was obtainable by an interposition between her own actual frontier and her enemies’ dominions of a number of half-subject dependencies.  Native princes were allowed to bear sway in the Punjab region, who acknowledged the suzerainty of Persia, and probably paid her a fixed tribute, but whose best service was that they prevented a collision between the Power of whom they held their crowns and the great mass of their own nation.

The Great Arabian Peninsula, which lay due south of the most central part of the Empire, and bordered it on this side for about thirteen degrees, or (if we follow the line of the boundary) for above a thousand miles, might seem to have been the most important of all the adjacent countries, since it contains an area of a million of square miles, and is a nursery of brave and hardy races.  Politically, however, Arabia