The Indus Valley's writing system has never been deciphered

The Bronze Age Indus Valley Civilization built precisely planned cities like Mohenjo-daro and Harappa around 2500 BCE, complete with covered drains and standardized weights. Despite thousands of surviving inscriptions on seals and pottery, no one has ever cracked its script, and scholars still debate whether it even encodes a spoken language.

— Andrew Robinson, The Indus: Lost Civilizations — Reaktion Books, 2015
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