trullo, conical, stone-roofed building unique to the regione of Puglia (Apulia) in southeastern Italy and especially to the town of Alberobello, where they are used as dwellings. Upon a whitewashed cylindrical wall, circles of gray stone, held in place by lateral opposition and gravity and without mortar, were piled to a pinnacle. Probably originating with a local Stone Age culture, the trulli have been perpetuated as a folk tradition, possibly because of the local shortage of lumber and the abundance of stone fragments that must be removed to permit land cultivation. Trulli are protected by Italian law as national monuments.