A trullo is an ancient stone building particular to Central Puglia. Rumour has it that the trulli were built as a tax dodge at a time when the local nobility was taxing permanent housing. Apparently they were pulled down with a rope and then reassembled once the tax man had left - one to be taken with a pinch of salt, especially after seeing a trullo! No two trulli have the same shape or dimension. This is because each trullo was built individually by hand. The external walls were built using the dry stone walling technique and can be up to 2m (6ft) thick as they consist of an inner and outer wall filled with the stones dug out when laying the foundations.It has a circular, or square base and a cone-shaped cupola usually finished with a whitewashed pinnacle. The pinnacles are made of hand-carved stone and, according to some people, represent the constructor's signature while others claim they have a symbolic meaning. The cupola was formed using specially hand cut stones (chianche) laid in slightly decreasing circles creating a balance requiring no cement. Because of the structure and materials used, a "thermos" effect is created inside the trulli so that the temperature remains warm in winter and cool in the hottest summer months. The symbols sometimes painted on the grey stone of the cupola are signs of good omen although their origins remain unknown. They may have been introduced by eastern settlers in Puglia, or be of Christian origin dating back to the first century.
(these notes were derived from Kevin & Carole's "Apppulia' website)