On this side nature had set no obstacles; and, if danger threatened, resistance had to be made by means of those artificial works which are specially suited for flat countries.
Long lines of wall, broad dykes, huge reservoirs, by means of which large tracts may be laid under water, form the natural resort in such a case; and to such defences as these alone, in addition to her armies, could Babylonia look in case of a quarrel with the Medes.

On this side, however, she for many years felt no fear.

Political arrangements and family ties connected her with the Median reigning house, and she looked to her northern neighbor as an ally upon whom she might depend for aid, rather than as a rival whose ambitious designs were to be watched and baffled.
Babylonia lay open also on the side of Arabia.

Here, however, the nature of the country is such that population must be always sparse; and the habits of the people are opposed to that political union which can alone make a race really formidable to others.

Once only in their history, under the excitement of a religious frenzy, have the Arabs issued forth from the great peninsula on an errand of conquest.