The IVC is sometimes called SSVC = Sarasvati Sindhu Valley
Civilization.
Sindhu = Indus.
The Sarasvati was a river which started as the Jumna / Yamuna
turning west across Punjab and/or Haryana and down what is now the
Ghaggar dry river bed into Pakistan and near Bahawalpur the Sutlej
joined it and it flowed down the Hakra and Raini Nala and Eastern
Nara channels and across the Rann of Kachchh to the sea. It dried up
around 1700BC due to its headwaters changing course.
It could be that the IVC died out because of:-
(1) Someone suggested a Tunguska-type asteroid impact.
(2) Too much intensive agriculture for too long without washing the
land through once in a while, and so the land salinated = got full of
salt.
Among the gods that the Rigveda worships are the [Asvina_] = "Two
Horsemen". They may represent the morning and the evening.
Someone wrote:-
>(VA) If the RV were to have inherited the Horse sacrifice from its
> IE background, ...
This horse sacrifice could merely be making a ceremony out of some
routine need to put a horse down because of illness or persistent
unmanageableness, or because they had more horses than they had feed
for. Recently an Anglo-Saxon warrior burial was found, and a horse
was buried with him, and the bones showed that the horse was useless
because it had severe arthritis in one of its feet.
The IVC might well have had a very big written culture, which has not
survived because the usual writing material in India (rectangles cut
from dried palm leaves) has not survived that long in the climate and
they did not use clay tablets.