Between the rivers: How the people of Mesopotamia established the first human civilisations

Sumeria cuts right through the heart of modern-day Iraq, as far south as the Persian Gulf, where it connects to the Indian Ocean. It was one of the first regions where mankind's new itch to control nature extended into the business of building artificial worlds in the form of cities and states. It is also where experts believe writing emerged.

Sumeria was a perfect dwelling place for early settled communities of humans. By 10,000 years ago, sea levels had risen by nearly 130m from their low point, and in this part of the world the climate was wetter, and therefore better for growing crops, than it is now. It is only in the last 5,000 years or so that temperatures have increased and rainfall reduced to make the Middle East the sandy, barren land that we know today.

A wetter climate was ideal for growing crops, such as wheat, barley and grapes that need winter rainfall. And just the right kind of wild animals – those perfect for domestication, such as goats, sheep and oxen – lived on the slopes and hillsides of the region. Such animals could be used as a source of food, as power for pulling ploughs and carts, and to provide raw materials for making clothes, bottles and leather goods.

The ancient region in which the first Sumerian cities emerged is called Mesopotamia. In Greek it means "between the rivers". The Euphrates and the Tigris proved ideal for supplying water to nearby land through systems of man-made irrigation channels, dykes, reservoirs and dams. These meant people could purposely flood their fields to provide just the right conditions for their artificially chosen crops to thrive. The river valley also provided a large, long, flowing superhighway to carry people and their possessions from one riverside city to the next.

It is now known that a writing system developed in ancient Sumeria about 5,000 years ago, thanks to a remarkable archaeological discovery made in the 1840s by a young amateur British archaeologist called Austen Layard. Layard discovered the remains of the ancient city of Nineveh, including many thousands of clay tablets and stone slabs inscribed with the obscure form of ancient writing that came to be known as cuneiform.

Probably the most famous tablets from the Nineveh hoard are those that tell us of the adventures of an early king of Sumeria called Gilgamesh. He ruled over one of the first Sumerian cities, called Uruk, situated on the east bank of the Euphrates (now in southern Iraq). At its height, as many as 80,000 people lived in Uruk, making it then the largest city in the world.

The tablets tell us an enormous amount about life in Ancient Sumeria, notably in The Epic of Gilgamesh, which, along with other stories found among the inscriptions, provides fascinating insights into how the Sumerian people viewed the world – including some of the first written evidence of religious beliefs.

The Sumerians believed that the gods met each New Year's Day to decide what fateful events would happen in the coming year. Their decisions resulted in all manner of disasters, such as droughts and floods, as well as unexpected good fortune like bumper harvests and military success. Aside from these annual fates everything else was, they believed, predetermined by the stars.

The Sumerians and their successors in Assyria and Babylon believed that the world rested on a flat disc, surrounded by water on all sides. Above the sky was a tin roof punctured with small holes through which the celestial fires of heaven could be seen. They studied these holes (the stars), and watched them rotate each night along a predictable path. They discovered that five large stars behaved in a different, unexplained way. They believed these were the stars of the gods – we know them today as the five planets visible to the naked eye: Mercury, Venus, Mars, Jupiter and Saturn.

The Sumerians dedicated one day of the week to each of the five randomly moving stars – with the Sun and the Moon, that made seven. The names we use in English, derived from the Latin language later used by the Romans, shows the legacy we still owe to the Sumerian system: Saturday (for Saturn), Sunday (for the Sun), Monday (for the Moon). The link is clearer in French for the other weekdays: Mardi (Mars), Mercredi (Mercury), Jeudi (Jupiter) and Vendredi (Venus).

The Sumerians constructed towers, called ziggurats, so they could be closer to the heavens. These were terraced pyramids built from sun-baked clay bricks. The top of each tower was flat, and a shrine or temple to a god would be built on it. Only priests were allowed inside them, since these were believed to be the dwelling places of the gods.

It isn't just our seven-day week that we owe to these ingenious people. They were also prodigious mathematicians. Amongthe clay tablets found by Layard is evidence of complex arithmetic, with different combinations of vertical strokes and V-shapes used to represent the numbers one to nine. The Sumerians developed a system of mathematics based on the number 60, because there are so many ways of dividing it up (by 2, 3, 4, 5, 6, 10, 12, 15, 20, 30).

Their genius for astronomy and mathematics was matched by their inventiveness at making things with their hands. These people are credited with inventing the wheel. These weren't used for carts or chariots, although they were to come soon after. They were wheels for making clay pots – pottery wheels. It didn't take long for the wheel to be adapted as a device for transporting goods. Tamed asses were used to pull the first carts. Solid wooden wheels were later replaced by spoked wheels that could carry more weight, making them ideal to support chariots of war.

Like all human civilisations, even the ingenious Sumerians could not survive forever. They learnt that living a life in one fixed location, rather than moving from place to place, as hunter-gatherers do, came at a considerable price. After many generations of intensive farming the land became less fertile, owing to increasing levels of salt which spread to the fields through artificial irrigation. To start with, the people responded by switching from growing wheat in favour of barley, which could tolerate higher salt levels. But before long, even that crop just withered away as the soil turned sour.

By about 2000BCE, the land around the mouths of the Euphrates and the Tigris had become impossible to farm, and cities such as Ur and Uruk fell into permanent decline.

Their misfortune meant opportunity for others. The mighty Assyrian king Sargon the Great (who ruled c2270–2215BCE) built one of the world's first empires around Akkad, a city located hundreds of miles further up the Euphrates, where the land was still rich and fertile. A seventh-century BCE clay tablet describes how Sargon's mother cast him off as a baby in a basket of rushes. Eventually, he was found and cared for by the king's water-drawer, Akki, and reared as his son. This echoes the story of Moses, who it is said in the Bible came from the Sumerian city of Ur.

As the southern Sumerian cities declined, they fell victim to Sargon's conquests, becoming part of his enormous new domain that stretched from south-west Iran to the Mediterranean coast. Cultures diffused two ways. While the Akkadian language gradually started to replace Sumerian cuneiform, the Sumerians' knowledge of craftsmanship and technology spread far and wide across the vast Akkadian empire.

By evolving a system of writing, the Sumerian civilisation allowed recorded history as we know it to begin. The written word meant that knowledge could be transferred, without error or change, from one part of the world to another, and from one generation to the next. It was one of the most potent tools for organising the construction and administration of man's first artificial worlds.

The man who found Gilgamesh

Modern knowledge of the civilisation of ancient Sumeria is largely attributable to a remarkable young British lawyer called Austen Layard (above). An amateur archaeologist, he decided in the 1840s that, rather than stick around in London to practise law, as was his training, he would head off for a life on the island of Ceylon (now Sri Lanka), which was then under British rule.

Layard never got to Ceylon. He stalled in the Middle East, in Persia, where he became fascinated by the history of the region, and in particular by a strange large mound near the town of Mosul, on the banks of the Tigris in Ottoman Iraq. He was so curious about this odd, man-made hill covered in dust and sand that he persuaded the British Ambassador in Turkey to pay for an archaeological dig to see what lay beneath it.

On 9 November 1845, Layard, with a team of local tribesmen, started excavations. Within hours their brushes and spades revealed the walls of an ancient palace covered with stone slabs, each one tightly inscribed with a curiously shaped form of unknown ancient writing.

This wasn't just a fancy royal palace with a few old graffiti marks that Layard and his team had stumbled across. After a series of excavations, two palaces and a huge royal library had been unearthed on the site, which turned out to be what remains of the ancient biblical city of Nineveh.

Layard and his team uncovered a staggering 20,000 clay tablets including king lists, histories, religious texts, mathematical and astronomical treatises, contracts, legal documents, decrees and royal letters, as well as the now-celebrated "Epic of Gilgamesh", which describes the adventures of an early king of Sumeria.

These tablets provide a fascinating insight into ancient times that has transformed our understanding of when and where the first civilisations emerged, and what they were like.