By Michael Wood
Last updated 2009-11-05
The decline of the Harappan civilisation remains a source of speculation. The theory of an Aryan invasion has long since been discredited and it is now widely believed to be due to climate change and perhaps also to tectonic activities. Major changes took place in the northern part of the Indian subcontinent causing its rivers to change course. Resulting water shortages led to the abandonment of many of the settlements as people started migrating eastwards.