A trullo (plural, trulli) is a traditional Apulian dry stone hut with a conical roof. Their style of construction is specific to the Itria Valley, in the Murge area of the Italian region of Apulia. Trulli were generally constructed as temporary field shelters and storehouses or as permanent dwellings by small proprietors or agricultural labourers. Their golden age was the 19th century.

From the casedda to the trullo The Italian term il trullo (from the Greek word τρούλος, cupola) refers to a house whose internal space is covered by a dry stone corbelled or keystone vault. Trullo is an italianized form of the dialectal term truddu used in a specific area of the Salentine peninsula (i.e. Lizzaio, Maruggio and Avetrana, in other words outside the Murgia dei Trulli proper) where it is the name of the local agricultural dry stone hut. Trullo has replaced the local term casedda (pl. casedde) (Italian casella, pl. caselle) which was used by locals in the Murgia to call this type of house.

A stonemason specializing in the building of trulli is a trullisto or trullaro in Italian. The corresponding dialectal term is caseddaro (caseddari in the plural), i.e. builder of casedde.

Distribution The style of construction is specific to the Itria Valley, in the Murge area of the Italian region of Apulia. Trulli may be found in and out of Alberobello, and in the areas around Locorotondo, Fasano, Ostuni, Cisternino, Martina Franca and Ceglie Messapica.

Masonry Traditionally trulli were built using dry stone masonry, i.e. without any mortar or cement. This style of construction is also prevalent in the surrounding countryside where most of the fields are separated by dry-stone walls.

Walls In Alberobello, the structural walls of a trullo are laid directly on the bedrock, after removal of the topsoil when necessary. Their width varies from 0.80 metres to 2.70 metres (a measure recorded in the Trullo Sovrano). Their height (from ground level to where the vault starts) ranges from 1.60 metres to 2 metres. Their exterior facing has a 3 to 5% batter.

Plans. The trullo may take on a circular or a square plan. The circular trullo is mostly a temporary shelter for animals and their fodder, or for the peasant himself. The trullo that is part of a grouping of three, four or five follows a squarish plan. It may serve as a kitchen, bedroom, animal shelter, store room for food or tools, oven, cistern as the case may be.

Roofs. The roofs are constructed in two skins: an inner skin of limestone voussoirs, capped by a closing stone, and an outer skin of limestone slabs that are slightly tilted outwardly, ensuring that the structure is watertight. The roof stones can be taken away without compromising the stability of the rest.

Interiors The vast majority of trulli have one room under each conical roof, with additional living spaces in arched alcoves. Children would sleep in alcoves made in the wall with curtains hung in front.

A multiroomed trullo house has many cones representing a room each.

Along with its exterior wall, a trullo's interior room and vault intrados were often rendered with lime plaster and whitewashed for protection against drafts.

The trulli used as dwellings all have an open fireplace complete with a flue (hidden in the masonry) and a stone-built chimney stack (rising high above the roof). Because of their design, trulli are difficult to heat: the walls are too thick and warm air will rise up the interior cone. An alternative heating solution was to use a central brasero with embers in it (a specimen can be seen in Alberobello's Museo del Territorio).

The thick stone walls and dome of the trullo, pleasantly cool in the summer, tend to become unpleasantly cold during the winter months, condensing the moisture given off by cooking and breathing and making it difficult to feel warm even in front of the fire. The inhabitants simply leave the doors open open during the day to keep the interior dry, and live more outdoors than in.

In trulli that were used as stables, the troughs the animals fed from can still be seen.

Windows Owing to the concentration of houses, trulli have few openings outside their doorway and a small aperture provided in the roof cone for ventlation.