The Indus Civilization (Cambridge History of India, Supplementary Volume) c8.3.2

c8.3.2

But the very use of costly baked bricks in lieu of the cheap mud-bricks usual in protohistoric Asia may be supposed to reflect a climate wet enough to necessitate the more durable material.¹ The Indus seals, with their vivid representations of tiger, buffalo, rhinoceros and elephant, are the work of artists to whom these marsh- or jungle-animals were familiar; alternatively, the extreme scarcity of evidence for the camel (p. 60) is consistent with non-desert conditions. The mere existence of the cities is indeed conditional upon a local fertility out of all relation to the present landscape and not wholly explicable by the possibility of elaborate former irrigation systems of which not a trace can be expected to survive on the present aggraded surface. A certain degree of climatic change is beyond dispute; but how far that change is due to "natural causes" and how far to sheer human improvidence (if that be other than a "natural cause") is less easy to say. History would suggest that the process of desiccation was already far advanced by the time of Alexander the Great, whose returning army was decimated in the cheerless wastes of Makrān. And it may be that an increasing aridity had already contributed to the downfall of the Indus cities. When we turn from fact to cause, difficulties accumulate.