The trulli, houses in limestone, are a typical structure widespread in the Itria Valley and, in particular, in the town of Alberobello, in Apulia. The trulli are traditional dry stone huts with a roof made of dry-set slabs and were originally conceived as temporary shelters or as permanent homes by small landowners or agricultural workers. These buildings have the characteristic of having a rectangular shape with a conical roof, made of set stones, covered with limestone to make it waterproof. The first appearances of these characteristic buildings date back to about a thousand years ago but only from the seventeenth century we can see their spread. Today we can count more than 1500 trulli, located mainly in the districts of Monti and Aja Piccola. Between 1909 and 1936 some of them became part of the monuments protected by UNESCO.