A trullo (plural, trulli) is a traditional Apulian stone dwelling with a conical roof. The style of construction is specific to Itria Valley (in Italian: Valle d'Itria), in the Murge area of the Italian region of Apulia (in Italian Puglia). They may be found in the towns of Alberobello, Locorotondo, Fasano, Cisternino, Martina Franca and Ceglie Messapica. Trulli were generally constructed as dwellings or storehouses. Traditionally they were built without any cement or mortar, thus avoiding taxation. This style of construction is also prevalent in the surrounding countryside where most of the fields are separated by dry-stone walls.
The roofs are constructed in two layers: an inner layer of limestone boulders, capped by a keystone, and an outer layer of limestone slabs ensuring that the structure is watertight. Originally, the conical structure would have been built directly on the ground, but most of the surviving structures are based on perimeter walls. In Alberobello atop a trullo's cone there is normally a pinnacle, that may be one of many designs, chosen for symbolism. Additionally, the cone itself may have a symbol painted on it (as shown in the picture of the trulli in Alberobello.) Such symbols may include planetary symbols, the malocchio (evil eye), the cross, a heart, a star and crescent, or quite a few others.
The walls are very thick, providing a cool environment in hot weather and insulating against the cold in the winter. The vast majority of trulli have one room under each conical roof: a multiroomed trullo house has many cones representing a room each. Children would sleep in alcoves made in the wall with curtains hung in front.
There are many theories behind the origin of the design. One of the more popular theories is that due to high taxation on property the people of Puglia created dry wall constructions so that they could be dismantled when inspectors were in the area.
Today the surviving trulli are popular among English and German tourists and are often bought and restored for general use. However, anyone wishing to restore a trullo needs to conform with many regulations as trulli are protected under the United Nations Educational, Scientific and Cultural Organization (UNESCO) world heritage law.