The Indus Valley Civilization was an ancient civilization in the Indian subcontinent which is discovered by archaeologists in 1920s. It was found as old as approximately 5000 B.C.E covering the areas of north-east Afghanistan to Pakistan and north-west India. It is named after the Indus Valley where the first remains were found. Before the excavation beginning 1861 there were no knowledge of the civilization that existed in the Indus Valley.
Satyug is the first of the four yugs, that is Satyug, Tretayug, Dwapara yug and Kaliyug. As described in religious books Satyug extends about 17,28,000 years when the people used to be of 32 feet height with age of about 1,00,000 years. This period was described as the golden period when there were no poor, no rich, no worldly desires, and no crimes. Originally only good path was created and all the human beings were permanently happy for ever. There was no trace of sorrow in their minds. But the people were bored due to continuous happiness so the Lord created the sin and gave freedom to souls to commit the sins.
Today, no existence of this yug is found on the earth. It seems that the remains of satyug have vanished. So the Indus Valley Civilization is considered to be the first civilization in India. But one day we might get some remains of Satyug which will prove it to be the oldest civilization.