What was unique about the indus valley settlements? which event likely caused the indus valley civilization to decline?

1. The Indus Valley settlements were not like the settlements of the other early civilizations. They were built on higher ground instead of the lower parts so that they can be protected from floods. The houses were built in the same manner and had the same sizes. The streets were made in strait lines and intersected in right angles. All of the houses had bathing areas and were connected to a sophisticated drainage system. Also, the settlements were not made for defense, as the civilization was a peaceful one.

2. It is still not clear as to why the Indus Valley civilization collapsed, but there are two theories that have a big support. One of them is that the Aryan people invaded the region, which corresponds with their migration tot he Indian subcontinent, and that their invasion destroyed this civilization. The problem with this theory is that there's not a single clue of war and destruction. The other theory is that the climate changes in this period changes the flows of the rivers, which resulted in failing crops year after year, and the civilization was not able to sustain itself anymore, thus dismantling into smaller divisions.