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. Underground cistern The stones needed for starting to build a trullo were provided by digging a cistern (cisterna), an absolute necessity in an area devoid of water. The cistern was capped with a lime-mortared barrel vault or dome that in many cases, supported the floor of the house. 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 may be taken away without compromising the stability of the rest of the building. 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, or cistern, as the case may be. In Alberobello, groupings did not exceed two trulli, as evidenced by nineteenth-century notarial deeds. Pinnacles In Alberobello, atop the cone of a trullo, there is normally a hand-worked sandstone pinnacle (pinnacolo), that may be one of many designs: disk, ball, cone, bowl, polyhedron, or a combination thereof, that is supposed to be the signature of the stonemason who built the trullo. Whitewashed symbols Additionally, the cone may have a symbol painted on it (as shown in the picture of the trulli in Alberobello.) Such symbols may include Christian symbols such as a simple cross, a cross on a heart pierced by an arrow (representing Santa Maria Addolorata ("Our Lady of Sorrows"), a circle divided into four quarters with the letters S, C, S, D in them (for Sanctus Christus and Sanctus Dominus according to one source, but more likely, the initials of Santo Cosma and Santo Damiano, the two saints to whom the local basilica is dedicated) and quite a few others. The symbols now visible on a row of trulli in via Monte Pertica (cross, pierced heart, host with rays radiating from