Persia seems never to have experienced any alarm of an Arab invasion; her relations with the tribes that came into closest contact with her were friendly; and she left the bulk of the nation in unmolested enjoyment of their independence.
Another country adjoining the Persian Empire on the south, and one which might have been expected to cause some trouble, was Ethiopia.

To Egypt Ethiopia had always proved an unquiet, and sometimes even a dangerous, neighbor; she was fertile, rich, populous; her inhabitants were tall, strong, and brave; she had a ready means of marching into Egypt down the fertile valley of the Nile; and her hosts had frequently ravaged, and even held for considerable terms of years, that easily subjected country.

It is remarkable that during the whole time of the Persian dominion Ethiopia seems to have abstained from any invasion of the Egyptian territory.

Apparently, she feared to provoke the power which had seated itself on the throne of the Pharaohs, and preferred the quiet enjoyment of her own wealth and resources to the doubtful issues of a combat with the mistress of Asia.
On her western horizon, clearly discernible from the capes and headlands of the Asiatic coast, but separated from her, except in one or two places, by a tolerably broad expanse of sea, and so--as it might have seemed--less liable to come in contact with her than her neighbors upon the land, lay the shores and isles of Greece--lovely and delightful regions, in possession of a brave and hardy race, as yet uncorrupted by luxury, though in the enjoyment of a fair amount of civilization.

As the eye looked across the Egean waters, resting with pleasure on the varied and graceful forms of Sporades and Cyclades, covetous thoughts might naturally arise in the beholder's heart; and the idea might readily occur of conquering and annexing the fair tracts which lay so temptingly near and possessed such numerous attractions.