What Caused the Rise and Fall of the Roman Empire: Water

It turns out that water may have played a major role in the rise and fall of the Roman Empire. Smart agricultural practice and an extensive grain-trade network allowed Romans to thrive in a water-limited environment. But  when the empire was pushed to the limits of its food resources, it eventually fell.

The Roman Empire stretched over three continents and spanned centuries. At its peak, it was home to an estimated 70 million people. Maintaining a stable food supply across such an expansive area, though, was no easy task-particularly given the variable and arid climate of the Mediterranean region.

"We can learn much from investigating how past societies dealt with changes in their environment," said Brian Dermody, one of the researchers, in a news release. "For example, the Romans were confronted with managing their water resources in the face of population growth and urbanization. To ensure the continued growth and stability of their civilization, they had to guarantee a stable food supply to their cities, many located in water-poor regions."

The researchers focused on determining the water resources required to grow grain, which is the staple crop of the Roman civilization. They also examined how these resources were distributed within the Empire. In the end, they found that it takes between 1,000 and 2,000 liters of water to grow one kilo of grain. Then, they simulated virtual water trade based on virtual-water-poor regions demanding grain from the nearest virtual-water-rich region.

The researchers found that the Romans' ability to link different environments of the Mediterranean through trade allowed their civilization to thrive. If grain yields were low in a certain region, for example, they could import grain from another part of the Mediterranean experiencing a surplus. Yet these same practices also contributed to their downfall; as urban centers grew, the Empire was pushed to its limits. In the long term, this eroded the Empire's resilience to poor grain yields arising from climate variability.

"We're confronted with a very similar scenario today," said Dermody. "Virtual water trade has enabled rapid population growth and urbanization since the beginning of the industrial revolution. However, as we move closer to the limits of the planet's resources, our vulnerability to poor yields arising from climate change increases."

The findings are published in the journal Hydrology and Earth System Sciences.