While thus consolidating his first conquest, Cyrus penetrated into the unknown regions of the far East. Nothing would have been easier for him than to have fallen upon Babylon and overthrown, as it were by the way, the decadent rule of Nabonidus; but the formidable aspect which the empire still presented, in spite of its enfeebled condition, must have deceived him, and he was unwilling to come into conflict with it until he had made a final reckoning with the restless and unsettled peoples between the Caspian and the slopes on the Indian side of the table-land of Iran. As far as we are able to judge, they were for the most part of Iranian extraction, and had the same religion, institutions, and customs as the Medes and Persians. Tradition had already referred the origin of Zoroaster, and the scene of his preaching, to Bactriana, that land of heroes whose exploits formed the theme of Persian epic song. It is not known, as we have already had occasion to remark, by what ties it was bound to the empire of Cyaxares, nor indeed if it ever had been actually attached to it. We do not possess, unfortunately, more than almost worthless scraps of information on this part of the reign of Cyrus, perhaps the most important period of it, since then, for the first time, peoples who had been hitherto strangers to the Asiatic world were brought within its influence. If Ctesias is to be credited, Bactriana was one of the first districts to be conquered. Its inhabitants were regarded as being among the bravest of the East, and furnished the best soldiers. They at first obtained some successes, but laid down arms on hearing that Cyrus had married a daughter of Astyages.* This tradition was prevalent at a time when the Achaemenians were putting forward the theory that they, and Cyrus before them, were the legitimate successors of the old Median sovereigns; they welcomed every legend which tended to justify their pretensions, and this particular one was certain to please them, since it attributed the submission of Bactriana not to a mere display of brute force, but to the recognition of an hereditary right. The annexation of this province entailed, as a matter of course, that of Margiana, of the Khoramnians,** and of Sogdiana. Cyrus constructed fortresses in all these districts, the most celebrated being that of Kyropolis, which commanded one of the principal fords of the Iaxartes.*** * This is the campaign which Ctesias places before the Lydian war, but which Herodotus relegates to a date after the capture of Sardes. ** Ctesias must have spoken of the submission of these peoples, for a few words of a description which he gave of the Khoramnians have been preserved to us. *** Tomaschek identifies Kyra or Kyropolis with the present Ura-Tepe, but distinguishes it from the Kyreskhata of Ptolemy, to which he assigns a site near Usgent.