Tides may have powered the rise of the world’s first cities

For more than a century, the standard story has held that Sumerian cities rose only after powerful rulers dug vast canal networks between the Tigris and Euphrates. Those canals unlocked large-scale agriculture and, with it, urban life.

But that timeline has always carried a quiet contradiction: how could dense communities form before the governments needed to run such massive irrigation systems?

A new study offers a compelling answer. Long before kings carved canals, early farmers may have tapped a natural, twice-daily force – the Tigris River’s tidal pulse.

By harnessing these predictable rises in water level, small villages could irrigate crops without state power, bureaucracy, or monumental engineering.

A core sample with a big story

To test the idea, researchers recovered a 82-feet (25-meter) sediment core from beneath Lagash – one of Sumer’s marquee cities – capturing more than 7,000 years of layered history.

The uppermost feet that archaeologists care about are usually missing from oil industry cores, which is why this “on-site” sequence is such a prize.

The earliest layers contained shells and marine debris, clear evidence that Lagash once sat far closer to the sea than it does today.

That proximity set off a new line of thinking. If the Persian Gulf’s shallow basin drove strong tides thousands of years ago, those pulses would have surged upriver, riding under the fresher surface flow.

“Saltwater is heavier than fresh, so it stays at the bottom and lifts the freshwater up,” said study co-author Liviu Giosan.

The result: a predictable, twice-daily rise in river level that small communities could divert onto fields without digging grand canals or erecting bureaucracy to match.

Tigris tides shaped early farming

If the Tigris rose and fell like clockwork – even hundreds of miles inland – then the first farmers had a reliable, low-tech water source for wheat, date palms, and garden crops. That flips the script on how urban density took root.

Instead of a top-down project ramming irrigation through deserts, early urbanism could have emerged from bottom-up clustering along tidally breathing channels.

The framework also helps explain the astonishing speed of settlement growth around Lagash. Annual spring floods shuttled fresh sediment downstream, periodically revealing new belts of fertile soil.

“You have fertile lands revealing themselves at almost generational speed,” said archaeologist Reed Goodman from Clemson University.

With steadier harvests came the social slack to experiment. Occupations could diversify, hierarchies could form, and administrative tools could evolve.

“You don’t experiment when you’re desperate, you experiment when you have a little wiggle room,” said University of Pennsylvania archaeologist Naomi Miller.

Tigris loss drives canal building

Of course, deltas don’t sit still. Over millennia, shifting channels and changing flood regimes dulled the tidal signal and eroded that effortless abundance.

Communities that had already sunk labor and identity into towns didn’t simply pack up. They engineered their way forward.

According to Goodman,, highly organized cities emerge as a response to trying to preserve this landscape. “Around 2500 B.C.E., the first kings in Lagash start talking about building large-scale canals.”

Thus, large-scale irrigation is not the spark of urbanism, but the sequel –  a civic response to a fading natural subsidy.

Fresh insight into early cities

If this model holds, it rewrites a century of assumptions about the state’s primacy in Mesopotamia’s origin story.

Jaafar Jotheri, a eoarchaeologist at the University of Al-Qadisiyah who wasn’t involved in the study, thinks the impact could be sweeping.

“This paper will revolutionize our understanding of Sumerian cities. Every Mesopotamian archaeologist should take a look at this,” said Jotheri.

The research also closes the chicken-and-egg loop that Goodman flagged. It shows how dense populations could assemble around a simple, repeating water rhythm long before complex administrations existed to manage canals.

Not everyone is convinced

Skeptics, though, raise fair cautions. City University of New York archaeologist Stephanie Rost argues that early irrigation features were effective precisely because they were modest, and that canals alone can’t explain state formation.

“At the time of the rise of the first cities and states, I don’t think irrigation systems were large-scale. Irrigation plays a role, but it’s not a prime mover,” she said.

Wetland abundance, including fish, reeds, and game, may have been enough to bankroll early urban experiments without invoking tides.

Jotheri also warns against stretching one site’s record too far across southern Mesopotamia and points to messy realities in the water column.

In real rivers, seawater and freshwater mingle so early farmers would have grappled with brackish conditions.

New blueprint for the first cities

Even with those caveats, the study’s core insight is powerful. Regular Tigris tidal forcing could have provided dependable, labor-light irrigation to pre-urban farmers, enabling population clustering without an empire of ditches and canals.

Later, as the delta shifted and that natural pulse weakened, rulers scaled up canal works to protect and extend a way of life already in motion.

That sequence – nature’s rhythm first, engineered systems second – offers a compelling new blueprint for how the earliest cities took hold on the Mesopotamian plain.

The research is published in the journal PLOS ONE.

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