The Persian Empire of Darius I, the first of the new Aryan empires in the seat of the old civilizations, was the greatest empire the world had hitherto seen. It included all Asia Minor and Syria, all the old Assyrian and Babylonian empires, Egypt, the Caucasus and Caspian regions, Media, Persia, and it extended into India as far as the Indus. Such an empire was possible because the horse and rider and the chariot and the made-road had now been brought into the world. Hitherto the ass and ox and the camel for desert use had afforded the swiftest method of transport. Great arterial roads were made by the Persian rulers to hold their new empire, and post horses were always in waiting for the imperial messenger or the traveller with an official permit. Moreover the world was now beginning to use coined money, which greatly facilitated trade and intercourse. But the capital of this vast empire was no longer Babylon. In the long run the priesthood of Bel Marduk gained nothing