Of the reign of Nabopolassar the information which has come down to us is scanty.  It appears by the canon of Ptolemy that he dated his accession to the throne from the year B.C. 625, and that his reign lasted twenty-one years, from B.C. 625 to B.C. 604.  During the greater portion of this period the history of Babylon is a blank.  Apparently the “golden city” enjoyed her new position at the head of an empire too much to endanger it by aggression; and, her peaceful attitude provoking no hostility, she was for a while left unmolested by her neighbors.  Media, bound to her by formal treaty as well as by dynastic interests, could be relied upon as a firm friend; Persia was too weak, Lydia too remote, to be formidable; in Egypt alone was there a combination of hostile feeling with military strength such as might have been expected to lead speedily to a trial of strength; but Egypt was under the rule of an aged and wary prince, one trained in the school of adversity, whose years forbade his engaging in any distant enterprise, and whose prudence led him to think more of defending his own country than of attacking others.  Thus, while Psammetichus lived, Babylon had little to fear from any quarter, and could afford to “give herself to pleasures and dwell carelessly.”

The only exertion which she seems to have been called upon to make during her first eighteen years of empire resulted from the close connection which had been established between herself and Media.  Cyaxares, as already remarked, proceeded from the capture of Nineveh to a long series of wars and conquests.  In some, if not in all, of these he appears to have been assisted by the Babylonians, who were perhaps bound by treaty to furnish a contingent as often as he required it, Either Nabopolassar himself, or his son Nebuchadnezzar, would lead out the troops on such occasions; and thus the military spirit of both prince and people would be pretty constantly exercised.

It was as the leader of such a contingent that Nabopolassar was able on one occasion to play the important part of peacemaker in one of the bloodiest of all Cyaxares’ wars.  After five years’ desperate fighting the Medes and Lydians were once more engaged in conflict when an eclipse of the sun took place.  Filled with superstitious dread the two armies ceased to contend, and showed a disposition for reconciliation, of which the Babylonian monarch was not slow to take advantage.  Having consulted with Syennesis of Cilicia, the foremost man of the allies on the other side, and found him well disposed to second his efforts, he proposed that the sword should be returned to the scabbard, and that a conference should be held to arrange terms of peace.  This timely interference proved effectual.  A peace was concluded between the Lydians and the Medes, which was cemented by a royal intermarriage:  and the result was to give to Western Asia, where war and ravage had long been almost perpetual, nearly half a century of tranquillity.