Indus Valley Script

Script of the Indus Civilization (Harappan civilization), 2600–1900 BC. Undeciphered for 4,000+ years — the only one of the world's four great ancient civilizations whose writing remains unread. Over 4,000 inscriptions have been catalogued on seals and tablets, yet a century of research has yielded 0% decipherment; average inscription length is just ~5 signs, and some scholars even question whether it constitutes true writing. The system uses ~400 signs. The key barriers to decipherment are the absence of a bilingual inscription and unknown underlying language. The Dravidian family hypothesis is the most favored but has not achieved scholarly consensus.