The trulli, typical limestone dwellings of Alberobello, are extraordinary examples of dry-stone slab constructions, a technique dating back to prehistoric times and still used in this region. Although rural trulli are scattered throughout the Itria Valley, the highest concentration of the best-preserved examples of this architectural form can be found in the town of Alberobello, with more than 1,500 structures. In 1996 they were included in the UNESCO list of World Heritage Sites.