The Senate has a number of powers which the House of Representatives (or any other institution) does not have.
These include: - consenting to treaties (international agreements), which is a condition for their later ratification - confirming appointments of a number of officials, such as the ambassadors, military officers, federal judges -trying government officials if they were impeached by the House
The interesting this about the people oft he Ancient Indus Valley is that the people seem to have just disappeared, and historians and archeologists cannot figure out what happened.