indus unicorn
Indus civilisation seal unicorn Royroydeb/CC

Experts from across the world are working to discover the secrets behind the enigmatic 4,000-year-old Indus script. The ancient Indus civilisation populated what is now Pakistan and north-west India for 500 years, between 2600BC and 1900BC, and it is thought to have been the most extensive urban societies of its period.

It had a population of an estimated one million people and had a huge maritime trade industry. But then it disappeared and remained hidden from history for thousands of years. After being rediscovered, cracking its script to learn more about the culture's history has been a challenge faced by hundreds of researchers around the world.

Andrew Robinson, who has written a book on the language and has been researching the subject for over 20 years, has looked at the progress currently being made on deciphering this lost language.

Writing for Nature magazine, he notes the script was first discovered in the 1920s by British and Indian archaeologists, who stumbled upon it by accident in ruins. One such settlement was Mohenjo-daro, which had sophisticated street planning, toilets and drainage system. It also had extremely well carved seal stones featuring the enigmatic script complete with pictograph signs, humans, animals and a unicorn.

Experts have argued the script could be an early form of Sanskrit or Dravidian, but problems arise from both theories. With no information about its base language, there is no starting point from which to begin as with other ancient scripts such as Mayan.

collection of indus seals
A collection of Indus seals CC BY-SA 3.0

But what do we know? Robinson writes Indus is written right to left, with the segments containing repeated sequences of characters. Estimates of the number of symbols in the script varies from between 400 and 950 – no seal stone has been found with more than 26 symbols, with most carvings averaging five. Almost all researchers agree the script has too many signs to be an alphabet or a system where signs represent syllables.

"As for the language, the balance of evidence favours a proto-Dravidian language, not Sanskrit," Robinson wrote. "Many scholars have proposed plausible Dravidian meanings for a few groups of characters based on Old Tamil, although none of these 'translations' has gained universal acceptance."

In terms of breaking the code, he said over 100 attempts to decipher the currently undecipherable have been published but that with ever more collaborations between archaeologists, linguists and digital experts, the possibility of discovering the secrets of the mystery script "looks possible" – if not some way off.

At present, less than 10% of the known Indus sites have been excavated. Indeed, with the civilisation being uncovered less than a century ago, many of its treasures remain hidden from view. And finding them in the troubled region where they lie adds further difficulties: Robinson added: "If these sites, and some others within Pakistan and India, were to be excavated, there seems a reasonable prospect of a widely accepted, if incomplete, decipherment of the Indus script."