More than 5,300 years ago, a civilization emerged along the lush basins of the Indus River in present-day northwest India and Pakistan. Its residents, mostly farmers and traders, lived in cities of baked brick, making it one of the world’s earliest urban civilizations.

But around 2500 B.C.E., residents migrated away from big cities like Harappa and Mohenjo-Daro—with estimated peak populations of 80,000 residents combined—and dispersed into smaller villages in the foothills of the Himalayas. Eventually, the Indus Valley civilization faded away.

It left behind artifacts and archaeological sites that have kept scholars busy for centuries—many featuring a mysterious script that nobody has been able to read.

The reason behind its demise remains a mystery, as do the rules and beliefs of the society, all possibly locked behind their yet-to-be deciphered language.

But the case is not closed, and Rao thinks that previous efforts to infuse the script with spiritual and religious meaning ignore the fact that the script has mostly been found on objects of commerce, according to BBC News. The typical layout includes signs running across the top of a seal with an animal figure underneath.