In the year 423 B.C. Darius Nothus ascended the throne of Persia. That country was then the greatest empire in the world, and had an area nearly equal to that of the United States. The capital of this seemingly powerful realm was the ancient city of Babylon on the lower Euphrates. Here the Great King, as he was styled, had his principal palace, from which he issued orders to his twenty or more satraps or governors whose provinces extended in name at least from the shores of the Mediterranean to the banks of the Indus, and from the Persian Gulf to the Black Sea.