A model of the ancient environment suggests a new theory about how some of the first cities in human history were built.

The research, published in PLOS One, proposes that the beginnings of urban civilisation in ancient Mesopotamia were driven by the dynamic relationships between rivers, tides and sediments at the head of the Persian Gulf.

The Sumerian civilisation was in the south of the region known as Mesopotamia in modern Iraq.

Sumer’s city-states of Ur, Uruk, Eridu and Lagash began to emerge around 7500 BCE, and were established by about 5,000 BCE.

While some “proto-cities” like Jericho and Çatalhöyük had emerged earlier, the Sumerian city-states are considered the cradle of civilisation because of the development of agriculture, writing and inventions such as the wheel which formed the cultural bedrock of these cities.

Other early cities in the Indus Valley and the Americas date to roughly 3000 BCE, and the first cities of Egypt emerged in about 5000 BCE.

The conditions which led to the formation of the first urban centres in Sumer have long interested archaeologists and anthropologists.

It has been thought that the fertile land provided by the deltas of the Tigris and Euphrates rivers enabled the critical development of large-scale agriculture necessary to support bigger, denser populations. But the new study shows that it was about more than just fertile soil.

“Our results show that Sumer was literally and culturally built on the rhythms of water,” study lead Liviu Giosan says in a press release. Giosan is a geologist at the Woods Hole Oceanographic Institution – an independent research organisation based in the US.

“The cyclical patterns of tides together with delta morphodynamics – how the form or shape of a landscape changes over time due to dynamic processes – were deeply woven into the myths, innovations, and daily lives of the Sumerians.”

The researchers used a combination of satellite imagery and drill cores to study the palaeoenvironment of southern Mesopotamia.

About 7,000 to 5,000 years ago, the Persian Gulf extended further inland than today. Tidal flows pushed freshwater far into the lower reaches of the Tigris and Euphrates twice a day. At this point in time, the Tigris and Euphrates had yet to form deltas.

Giosan and co-author Reed Goodman, from Clemson University in the US, say the ancient Sumerians may have learned to harness this hydrological cycle using short canals to irrigate crops and date groves.

Once deltas formed at the head of the Gulf, the effect of the tides was cut off. This would have created a crisis for the ancient Sumerians which they needed to resolve to maintain their city-states.

Iraqi Marsh Arabs poling mashoofs, traditional canoes, loaded with freshly cut reeds. Credit: Reed Goodman, Clemson University.

The ancient people responded with extensive works for irrigation and flood protection which led to the so-called “Golden Age” of Sumer which began about 2100 BCE.

“We often picture ancient landscapes as static,” says Goodman. “But the Mesopotamian delta was anything but. Its restless, shifting land demanded ingenuity and cooperation, sparking some of history’s first intensive farming and pioneering bold social experiments.”

The shifting waters of ancient Mesopotamia also had societal and cultural impacts.

“The radical conclusions of this study are clear in what we’re finding at Lagash,” adds Holly Pittman, Director of the Pennsylvania Museum’s Lagash Archaeological Project, who is not an author on the paper. “Rapid environmental change fostered inequality, political consolidation, and the ideologies of the world’s first urban society.”