It is a mystery civilisation that has baffled the archaeological world for decades.

The Indus - the largest yet least known of all the first great urban cultures - thrived from 2600 to 1900 BC, and then abruptly vanished from historical records.

Very little is known about the people, who strangely left no archaeological evidence of warfare and communicated in one of the world's most complex scripts

Now, one expert believes we may be closer to deciphering the ancient script using digital technology that can find patterns in its unusual symbols.

The Indus - the largest yet least known of all the first great urban cultures - thrived from 2600 to 1900 BC, and then abruptly vanished from historical records. Pictured is a seal found in one of the known Indus settlements engraved with the motif of an animal and various symbols that researchers are still trying to decipher

THE INDUS PEOPLE: KEY FACTS The Indus civilisation - also known as the Harappan civilisation - thrived from 2600 to 1900 BC. Along with Ancient Egypt and Mesopotamia, it was one of three early civilisations of the Old World. The Empire stretched from the Arabian Sea to the Ganges, over what is now Pakistan, India and Afghanistan. At its peak, the civilisation may have had a population of more than 5 million, making up 10 per cent of the world's population. Among their settlements, researchers have uncovered the world's first known toilets, along with complex stone weights, drilled gemstone necklaces and exquisitely carved seal stone. Etched in of these artefacts is an unusual and complex script, which researchers are racing to decipher. Advertisement

Writing an in-depth report in Nature, Andrew Robinson, author of 'The Indus: Lost Civilizations', says research on the empire has progressed dramatically.

The Indus Empire stretched over more than a million square miles across the plains of the Indus River from the Arabian Sea to the Ganges, over what is now Pakistan, northwest India and eastern Afghanistan.

Like their contemporaries, the Indus - who may have made up 10 per cent of the world's population - lived next to rivers, owing their livelihoods to the fertility of annually watered lands.

But the remains of their settlements are located in a vast desert region far from any flowing river.

They were forgotten until the 1920s, but since then, a flurry of research has uncovered a sophisticated urban culture with myriad internal trade routes.

So far, more than a thousand Indus settlements covering Pakistan and northwestern India have been discovered.

The two largest settlements are Mohenjo-daro found and Harappa near the Indus river.

'They hosted the world's first known toilets, along with complex stone weights, elaborately drilled gemstone necklaces and exquisitely carved seal stones,' writes Robinson in his report.

Etched into these artefacts is an indecipherable script made up between 400 and as many as 600 distinct Indus symbols, including what some scientists describe as a 'unicorn'.

'Once seen, the seal stones are never forgotten. I became smitten in the late 1980s when tasked to research the Indus script by a leading documentary producer,' Robinson recalls.

'He hoped to entice the world's code-crackers with a substantial public prize.'

The two largest settlements are Mohenjo-Daro found and Harappa near the Indus river. Pictured is the Siddikui area of the ancient Indus Valley civilisation of Mohenjo-Daro

The Indus Empire stretched over more than a million square miles across the plains of the Indus River from the Arabian Sea to the Ganges, over what is now Pakistan, northwest India and eastern Afghanistan

Collectively, the academic world has published more than 100 attempts at solving the script, and now, researchers may be close to finally uncovering its meaning.

For instance, in recent years, the direction of writing — from right to left — has been revealed by studying character position in different inscriptions.

Robinson notes that the Technical University of Berlin, has created the first, publicly available, electronic corpus of Indus texts.

Meanwhile, computer scientist Rajesh Rao at the University of Washington in Seattle has been using digital analysis to find patterns in the symbols.

WERE THE INDUS WIPED OUT BY CLIMATE CHANGE? No one yet knows why such a great civilisation disappeared. Pictured are the remains of the Granaries of Harappa, Pakistan No one yet knows why such a great civilisation disappeared. One theory, which emerged in 2012, is that climate change led to the collapse of the ancient Indus civiliSation more than 4,000 years ago. A study also resolves a long-standing debate over the source and fate of the Sarasvati, the sacred river of Hindu mythology, the authors believe. Over five years an international team combined satellite photos and topographic data to make digital maps of landforms constructed by the Indus and neighbouring rivers. They then probed in the field by drilling, coring, and even manually-dug trenches and samples were tested. Co-author Dorian Fuller, an archaeologist with University College London, said: 'Once we had this new information on the geological history, we could re-examine what we know about settlements 'This brought new insights into the process of eastward population shift, the change towards many more small farming communities, and the decline of cities during late Harappan times.' The study suggests the decline in monsoon rains led to weakened river dynamics, and played a critical role both in the development and the collapse of the Indus culture. Advertisement

The team has calculated the amount of randomness in the script using the computer programming language Fortran.

They've found the Indus script seem to be most similar to those of Sumerian cuneiform.

But deciphering the script is not just an intellectual puzzle, it has also become deeply intertwined with the cultural history of South Asia.

'In fact, the script has become a battleground of sorts between three different groups of people,' Rajesh Rao, an Indus expert at Washington University said in a Ted Talk.

'First, there's a group of people who are very passionate in their belief that the Indus script does not represent a language at all.

'There's a second group of people who believe that the Indus script represents an Indo-European language.

The left image shows the remains of an Indus settlement in the Sahiwal District of Pakistan. The right image is of an artefact found among its ruins

THE FIRST EVER TOILET One of the biggest known accomplishments of the Indus civilisation was the invention of the world's first toilet. In Mohenjo-daro, one of the largest Indus sites in Pakistan, archaeologists have discovered what look like brick lined toilets. They have also found pipes protruding from the ground, which could been used as ancient urinals, along with small bathing platforms. The toilets and baths were connected to a brick drainage system that ran along the streets. They were also covered by bricks to disguise them from view. Waste would have been flushed away using water. Advertisement

'There's a last group of people who believe that the Indus people were the ancestors of people living in South India today.'

Along with the difficulty in deciphering the text, no one yet knows why such a great civilisation disappeared.

One theory, which emerged in 2012, is that climate change led to the collapse of the ancient Indus civilization more than 4,000 years ago.

A study also resolves a long-standing debate over the source and fate of the Sarasvati, the sacred river of Hindu mythology, the authors believe.

Over five years an international team combined satellite photos and topographic data to make digital maps of landforms constructed by the Indus and neighbouring rivers.

They then probed in the field by drilling, coring, and even manually-dug trenches and samples were tested.

The toilets and baths (pictured) were connected to a brick drainage system that ran along the streets. They were also covered by bricks to disguise them from view. Waste would have been flushed away using water

=These copper spearheads are from the Indus Valley civilisation and are currently housed in the National Museum of New Delhi. | Location: National Museum of New Delhi. If the remaining sites could be excavated, then researchers may finally unravel the secrets to the Indus script

Co-author Dorian Fuller, an archaeologist with University College London, said: 'Once we had this new information on the geological history, we could re-examine what we know about settlements

'This brought new insights into the process of eastward population shift, the change towards many more small farming communities, and the decline of cities during late Harappan times.'

The study suggests the decline in monsoon rains led to weakened river dynamics, and played a critical role both in the development and the collapse of the Indus culture.

Whatever happened, there remains a great deal to be unearthed about this great civilisation.

'On the ground in Pakistan and India, more inscriptions continue to be discovered — although not, as yet, any texts longer than 26 characters,' said Robinson.

'Unfortunately, less than 10 per cent of the known Indus sites have been excavated. The difficulty — apart from funding — is the politically troubled nature of the region.

If the remaining sites could be excavated, then researchers may finally unravel the secrets to the Indus script.