The Indus Civilization (Cambridge History of India, Supplementary Volume) c14.2

c14.2

As at present known, fortifications at the two major cities are confined to the citadels; it is not apparent that the Lower City was in either instance fenced. This in itself suggests that the function of the armed citadel may have been as much the affirmation of domestic authority as a safeguard against external aggression. Until, however, the negative evidence in respect of the Lower City is stronger than it is at present, too much stress may not be laid upon this interpretation.