The 'tuff' guide to the city of Caesar

The Seven Hills of Rome
July 14, 2006

Ever wondered why Martius in Titus Andronicus became so easily trapped in a hole in the ground? Shakespeare might not have been a trained geologist but he seems to have known that the Eternal City was built, literally, on loose foundations. Indeed, much of the success of Ancient Rome may be due in large part to its subterranean heritage. Need more convincing? Then take a look at The Seven Hills of Rome , a cleverly crafted historical supplement-cum-practical geological tour of this most famous of cities.

The scene is set by examining the city and surrounding landscape centred on the Trevi fountain and progressively pulling back in scale until we see Rome as a speck in the Central Italian peninsula, a town in the coastal plains dominated by the Apennine Mountain belt to the east and source of much of the city's water. But the real novelty lies in the final chapter comprising three field trips around the centre of Rome that can be followed on foot. The reader is encouraged to grab a map and take to the streets, using the book to explore the renowned buildings, stonemasonry and hydrogeology of the city.

Each page reveals new morsels of information. For example, "tuff", a generic term in geology used to describe the rock products of explosive volcanic eruptions, is derived from the Latin tufo meaning rock that can be cut by a knife. The easy way in which the stone could be quarried lead to a second, subterranean city - an underground Rome, a complex labyrinth of ancient tunnel-ways, known famously as the Catacombs. Although many are now accessible to the public, they pose a collapse hazard and systematic mapping is needed to reveal their full extent. There are a few locations, for example the southern base of Capitoline Hill, where it is still possible to examine pyroclastic flow deposits at first hand.

A different rock type, travertine, holds a special place in Rome's architectural history. This material, similar to marble but with a distinctive pockmarked texture, is found throughout the city in ancient buildings, Renaissance sculptures and modern hotels. The stone is formed by the build-up of layers of calcium carbonate precipitated from groundwater.

The book also shows how important it is for civil engineers to take on board the local geology or suffer the consequences. Rome has had its fair share of earthquakes over the millennia, and more are to come. The Parthenon, the world's earliest concrete structure, is made from pozzolan , a mix of crushed tuff and lime that gives it remarkable strength and longevity. By contrast, the Colosseum, whose southern side is built on loose river sediment filling an ancient creek, has fared poorly.

Thanks to this guide I have also overcome a lingering ignorance concerning the Seven Hills themselves. Visiting Rome in the 1990s, I expected to see peaks akin to Arthur's Seat in Edinburgh dominating the cityscape. Instead I was left wondering who had removed them. Not any more - these subtle features were there all along, the remnants of a tuff plateau formed from pyroclastic flows originating in the nearby Alban Hills during a period of explosive volcanic activity. The deposits altered the course of the Tiber, forcing it to flow towards the West. The hills are the eroded lobes of the plateau carved out by the action of running water.

It is clear that the authors, all eminent in their field and including a past president of the International Association of Volcanology, have enjoyed writing this book - its enthusiasm flows like the Tiber itself.

Even if the link between the geology of Rome and its development as a premier city in the ancient world is not as utterly compelling as the writers would have us believe, the book is nonetheless a delightful addition to the plethora of tourist information on the Eternal City.

Nick Petford is pro vice-chancellor for research and enterprise, Bournemouth University.

The Seven Hills of Rome: A Geological Tour of the Eternal City

Author - G. Heiken, Renato Funiciello and Donatella De Rita
Publisher - Princeton University Press
Pages - 245
Price - £18.95
ISBN - 0 691 06995 6

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