Theory:

Indus valley civilisation is also known as the Harappan civilisation. This is the earliest known urban culture of the Indian subcontinent. Harappan civilization dates back to \(2500\)–\(1700 BCE\), though the southern sites may have lasted later into the \(2^n\)\(^d\) millennium \(BCE\).
 
indus map.jpg
The Harappan civilisation or Indus valley civilisation was first discovered in \(1921\) in Harappa, Punjab, and then in \(1922\) in Mohenjo-Daro, Sindh, near the Indus River. Both of these places are in the provinces of Punjab and Sindh. In \(1980\), UNESCO designated the Mohenjo-Daro ruins as a World Heritage Site.
The relics of this civilisation were also found as far as Sutkagen Dor in southwestern Balochistan province, Pakistan, near the shore of the Arabian Sea, west of Karachi and at Ropar, also known as Rupar, in eastern Punjab state, northwestern India, at the foot of the Shimla Hills.
The Harappan civilisation is known for its two large cities, Harappa and Mohenjo-Daro, which consists of more than \(100 \)towns and villages. Overall, the two towns were about a mile square in area. They had very organised and centralised political powers, either in two large states or a single great empire with alternate capitals. It is also possible that Harappa succeeded Mohenjo-Daro, which is known to have been devastated more than once by floods.
 
On the Kathiawar Peninsula and beyond, the southern region of the civilisation appears to be of later origin than the significant Indus sites. The culture was literate, and its script has been tentatively deciphered, with \(250 \)to \(500 \)characters, and the language has been known as Dravidian.
Reference:
https://cdn.britannica.com/s:700x500/99/1599-050-131E38FE/sites-Indus-civilization.jpg