Matera has gained international fame for its ancient town, the "Sassi di Matera" (meaning "stones of Matera"). The Sassi originate from a prehistoric (troglodyte) settlement, and are suspected to be some of the first human settlements in Italy. The Sassi are houses dug into the tuff rock itself, which is characteristic of Basilicata and Puglia. Many of these "houses" are really only caverns, and the streets in some parts of the Sassi often are located on the rooftops of other houses. The ancient town grew in height on one slope of the ravine created by a river that is now a small stream. The ravine is known locally as "la Gravina". http://en.wikipedia.org/wiki/Matera