Rocks of Ages: We All Know Geology Has Shaped the Earth's Surface. but, as a New BBC TV Series Reveals, around the Mediterranean It Has Also Changed the Course of Human History

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Perched atop a hill overlooking the azure waters of the Gulf of Corinth, geologist Dr lain Stewart was armed only with a Mars bar and two books. He was explaining how the ancient Greek city of Heliki, thought by some to have inspired Plato's Atlantis, was suddenly destroyed one night in 373 BC. The ancients believed it was Poseidon's fury, but with geology as our guide, we had evidence to the contrary.

Stewart's chocolate bar represented the southern end of the Eurasian plate, which tectonic movement had stretched to create the Heliki Fault. The books were to be the two sides of the fault itself, which still have a habit of moving. Pushing the books over at an angle, Stewart demonstrated how, during seismic activity, the rock of the fault goes up on one side and on the other suddenly plummets. It was this geological action that allowed the waters of the Mediterranean to rush in and drown the ancient city.

I was in Greece as part of a team filming a new series for the BBC about geology. Travelling the length and breadth of the Mediterranean, we were proposing a bold thesis--that the geology of the region was responsible for shaping some of our greatest ancient civilisations and, indeed, life as we know it. Studying the rocks beneath our feet can enrich our knowledge of the history of a variety of subjects, from architecture and art to the fall of the great empires.

My first job was to tackle the distinctive architecture of the ancients. Why did the Egyptians favour pyramids and the Greeks mostly rectangles, but the Romans build pretty much any shape they liked? The answer lay in the different rocks each civilisation found on its doorstep.

Fifty million years ago, Egypt was covered by the vast Tethys Sea. As the sea's inhabitants died, the hard parts of their bodies accumulated on the seabed and were slowly transformed into sedimentary rock, namely limestone. This limestone layer was subsequently pushed up to become the bedrock of northern Egypt, a rock already cracked into chunks by tectonic action and readily available to build the great pyramids at Giza.

Sedimentary rocks such as limestone and sandstone have simple properties. They are formed in horizontal layers, rather like a wafer biscuit, which keep them compressed and produce a strong building material. To build on a large scale, it's important to spread the load, and the most effective way to do so is to have few blocks at the top and many at the bottom, which, of course, produces a pyramid.

The shore of the ancient Tethys Sea was located around what is now Luxor. Here ancient builders used the sandstone formed from that shore almost exclusively to build the vast Temple of Amun at Karnak 4,000 years ago. To support its giant stone roof, they used posts and lintels. But the nature of their chosen building material made this tricky. If sedimentary rock is turned through 90[degrees] and stood upright, the integral layers are no longer being compressed and the stone will just crumble. The solution was to make columns by stacking sandstone with its layers aligned horizontally and then rounding off the edges. However, sandstone is relatively fragile, so if these columns were placed too far apart, the roof slabs would crack. So it seems that it was more down to geology, rather than aesthetics, that the temple's famous Great Hypostyle Hall was filled with more than 130 giant columns.

In the ancient Greek capital of Athens, we worshipped at the altar of a different rock. The Parthenon is the jewel in the crown of ancient Greek architecture. Completed in 438 BC, it took nine years to build and was dedicated to the Goddess Athena. Its wonderfully ornate carvings and slender columns made it the most elegant building of its day. That its architects were able to achieve this level of elegance can be attributed to the special properties of marble.

The ancient Greeks didn't have to look very far for top-quality building material. …