Archaeologists have discovered evidence that the people who lived in Mesopotamia 4,000 years ago were able to make synthetic rock.

They needed stone for grinding corn but had no naturally occurring rocks in the region.

The fertile silt plains of the Euphrates and Tigris rivers in Mesopotamia, the area now mostly covered by modern day Iraq, gave rise to one of the great civilizations in the ancient world.

The river silts were ideal for growing crops particularly as there were no rocks in the soil. But without rocks, corn could not be ground for two of the greatest Mesopotamian inventions, beer and bread.

Rocks were imported from Iran or Turkey, but this involved a 1,000 kilometre journey.

So Mesopotamians started making their own - an artificial material with similar properties to the hard volcanic rock, known as basalt.

Heating up river silt

Archaeologists have discovered large, rectangular slabs of artificial basalt near the remains of the main temple of Mashkan-Shapir, a city of 15,000 inhabitants built on the banks of the river Tigris, 80 kilometres south of Baghdad.

The artificial rocks were made of river silt that had been heated to about 1,200C degrees, the highest temperatures that can be reached outside modern blast furnaces.

They were then cooled slowly to allow time for crystals to grow into a coarse, strong structure.