by Frank Carlson

There is something oddly attractive about a place slated to disappear, and at first glance, Civita di Bagnoregio is just that: a charming medieval town in central Italy that, thanks to its geology, has been slowly crumbling for thousands of years.

The Etruscans chose the site for its high ground in the 6th century B.C., but much of that ground has since fallen away. Civita di Bagnoregio is built on what's known as "tuff," volcanic rock over a bed of soft clay and sand. 

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Source: http://www.pbs.org/