Happy Valley: How a different ancient civilisation devoted itself to fertility, trade and equality

Not many people can genuinely claim to have discovered a lost world. But one day in 1827 a British spy called Charles Masson had the privilege of becoming one of them. He left his army base in Agra, India, site of the world famous Taj Mahal, and headed westwards with a fellow soldier on some unknown errand – it is even possible he may have been deserting.

On his journey he stumbled across the ruins of an ancient city at a place called Harappa, now situated in north-east Pakistan, which included what looked like a castle on top of a hill. Lying on the ground he found jewels, bangles and arm rings, as well as the remains of three ancient chariots. Masson knew he had disovered something extraordinary, but it wasn't until a hundred years later that professional excavations revealed the full extent of this lost civilisation, hidden for thousands of years beneath the mud, sand and dust.

Serious archaeological excavations began in the 1920s. They revealed that Harappa was one of the largest cities in what is now called the Indus Valley civilisation. More than 2,500 different sites have since been discovered. These settlements were established at about the same time as the first towns and cities of ancient Egypt and Sumeria – that is, starting from about 3300BCE. Over about 1,700 years, people living here developed what many experts consider was the most advanced and impressive society on Earth at the time. Then, quite suddenly, they vanished, seemingly into thin air. To this day, no one knows exactly why or where they went.

The people who lived here arrived from an ancient settlement called Mehrgarh, located near a town called Sibi in modern-day Pakistan. From about 2600BCE the landscape dried up as the climate changed and these people moved northward to the more fertile river valley of the Indus. By the end of the second millennium BCE people living in the Indus Valley had built a number of stunning cities. They contained many of the features we associate with modern living, making them unique in the world at that time.

These people were brilliant town planners. Their streets were designed in convenient, well-measured grid patterns, like a modern American city. Each street had its own sewerage and drainage systems which were, in some people's opinion, more advanced than many found in modern-day Pakistan and India.

Excavations have unearthed a series of large public buildings, including assembly halls and a meeting place for up to 5,000 citizens. Public storehouses, granaries and bath houses were surrounded by colonnaded courtyards. Indus Valley builders even used a type of natural tar to stop water from leaking out of what is almost certainly the world's first ever artificial public swimming pool. Underneath one house there are remains of what looks like an underfloor heating system, pre-dating the famous Roman hypocaust system introduced more than 2,000 years later.

Each house had access to a well, and waste water was directed to covered drains which lined the main streets. Some houses opened on to inner courtyards and small lanes, and for the first time houses were built on more than one level. The people wove cotton, fired exquisite pottery and crafted copper and bronze for making jewellery and statues. Metal workers lived here in abundance. Evidence of at least 16 copper furnaces have been uncovered in Harappa alone.

But unlike in Egypt and Sumeria, there is a noticeable absence of royal tombs. There are no ziggurats, pyramids, temples or big palaces characteristic of a rich, dominant ruling class. What makes the Indus Valley civilisation so interesting is that it suggests a way of life which was organised and efficient, but above all egalitarian. Most people, it seems, shared their wealth and lived in comparative equality.

This civilisation was based on trade, because it needed access to raw materials such as copper and tin from other places. One Indus Valley city, called Lothal, featured a massive artificial dock with a dredged canal and loading bays for filling and emptying ships.

Everything about this world of the Indus Valley seems to have been far before its time – from the sanitation of its streets and the central heating of its houses to the fabulous dockyards and meticulous works of art. Craftsmen and women were on a par with farmers, tradesmen – even priests. They all seem to have worshipped what is known as a mother goddess, which accounts for the hundreds of female figurines, including an exquisite small bronze dancing girl, found in sites throughout the region.

Plenty of evidence suggests that until about 4000BCE, and in some areas until 1600BCE, much of Europe and the Near East lived in a similar way.