How Was Alberobello Built

A trullo is a specific and quite demanding piece of engineering, and every element of it does a job.

Dry stone, no mortar

The roof is a corbelled dome: successive rings of stone, each cantilevered slightly inward over the one below, closing at the top with a single locking stone. Nothing binds them but their own weight and the accuracy of the fit. It is not an arch and uses no centring; it is a technique thousands of years older than the town.

Two shells

The cone is built as a double skin. An inner vault of roughly worked stone carries the load, and over it lies an outer skin of chiancarelle, thin flat limestone slabs laid overlapping like tiles so that rain runs off the outside without ever reaching the inner dome. Between the two is a packing of rubble.

The cistern

The whole roof is a catchment. Rain runs off the chiancarelle, is caught at the eaves and channelled down into a cistern cut into the rock beneath the floor. On a plateau with no surface water this was not a convenience but the condition of living there.

Walls and whitewash

The walls are massively thick, often well over a metre, which keeps the interior cool in summer and holds warmth in winter. They are limewashed white; the roofs are left bare grey stone.

What damages them

The commonest harm done to a trullo now is a well-meant repair in cement. A dry-stone cone works because it breathes and moves slightly; sealing it with mortar traps moisture inside the shell and the inner vault rots from within. Proper restoration means relaying stone, not gluing it.

The pinnacle

Each cone is finished with a carved pinnacolo — a disc, ball, cone or combination. They are often said to identify the builder. One room, one cone: a larger house simply means more cones joined together.