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House in Cene (1993-95) designed by Antonio Citterio e Terry Dwan

On numerous occasions we have wondered about the utility of analysing ancient walls in terms of their significance for contemporary architecture. We have asked ourselves this question prior to any further discussion of present-day masonry walls in order to try and understand the potential importance of stone materials currently available to architects: during the first part of the present chapter, we began by discussing the architectural role of stone in expressing the masonry “formulae” invented by the inhabitants of the ancient world, so as to be able to link this up to, and compare it with, the use of stone in contemporary architecture, without wishing to present a purely nostalgic account, while at the same time attempting to conserve the meaning, and the technical and architectural characteristics, of the original forms of masonry wall.
The constituent elements of stone can hardly be considered to have changed in recent times; indeed, as Nietzsche claims in his work ‘Human, all-too-human’: “Stone is more stone-like than it was before”. Stone reappears in a never-ending present, recognisable as, and identical to, its past form; stone that awaits, today like in the past, to be interpreted, utilised and valorised for what it is.
In an age in which materials seem to lose their very consistency, are made thinner and lighter than ever – sometimes to the point where their very essence seems to be negated – the “stoniness of stone”, its material compactness and heaviness, still gives it a meaning which may be taken for granted, but which in truth underlines the true essence and authentic quality of this precious material.
The underlying logic of building with stone, regardless of the specific initial geometrical configuration, remains that of the “heaping” and “linking” of the masonry: from the static point of view, the important thing is that the materials observe the tried and tested rules of “binding”, the result of centuries of building experience.
However, while the assembling and stratification of the material represents the “constructive essence”, there is always a need to interpret the methods by which walls are built, corners are created and masonry is arranged around openings; in other words, the techniques employed to create the configuration of the wall – that is, its “architectural essence”. The updating of contemporary masonry focuses more on this “architectural essence” than on any set of rigid rules (or, more realistically speaking, of rules to be abided by and passed on from generation to generation). In order to present a clear picture of contemporary wall design and construction, we are initially going to be examining the use of stone in its rough, unrefined state, in order to get an idea of the continuity and innovation witnessed from the ancient past to the present day. Sometimes the images of contemporary architecture will be used in this, the second section of the chapter on Stone Walls, to reinforce and give substance to our hypotheses – often illustrating what proves difficult to describe using mere words.

Court offices in Alba, Italy (1982-87) designed by Gabetti e Isola together with Guido Drocco

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Stone in its raw state, that is, as it is found in nature prior to being dressed and “refined”, has continued to be employed in architecture in the construction of what we may call irregular walls, where the stone elements (of varying shapes and sizes according to their natural state or after the very minimum of dressing) are not laid in regular horizontal courses, as they would be in the case of regular walls, but are matched and laid in the best possible way in order to create an “aggregate”, that is, an irregular composition with the fewest number of empty spaces.
The nature of walls is strongly influenced by the type of stone chosen (in terms of its mineralogical and geological characteristics). It is the nature of stone, rather than its working or its arrangement, that gives architectural specificity and figurativeness to the stratification of the wall, or rather, to the parietal aggregate (we believe this term to be the most appropriate expression for the technical system underlying irregular masonry walls).
Rough stone offers a variety of compositional options ungoverned by codified rules. The adjacency, touching and superimposition of the stones’ edges gives rise to indeterminate geometrical compositions, where the irregular stones (generally different from each other – with their own “personality”) form heterotopic structures characterised by stratification and reciprocal interconnection. This irregularity, this relative “instability”, explains the thickness of such walls, that is, their mass and depth which can be seen in doorways and in openings in general.

Morbegno Library (1965) designed by Luigi Caccia Dominioni

Irregular masonry “recounts” the story of the stone, of the geological characteristics of the place where the material used for construction originated from. In such cases, we find ourselves faced with the “generosity” of nature itself, with the variegated range of rough stones (either erratic or quarried), of boulders with perfectly parallel faces, or – in those areas crossed by rivers and streams – of large pebbles smoothed and rounded by the water’s action.
The rustic character of irregular masonry often displays patterns in which the material itself – the stone – expresses the architectural value of the construction, through the consistency of the stones themselves, their reciprocal interpenetration and their weaving an overall design.
The simplicity and naturalness of the connecting elements are what characterise, more than anything else, this extensive category of walls that despite being less elegant, are not without their own distinctive character and architectural vigour.
The fascinating character of poorer stone materials – often quarried or found locally, and thus strongly representative of the local landscape and history – is often transposed to these sober stone wall designs, and their intrinsic beauty is indeed difficult to describe. This is perhaps why architectural manuals and other written works seldom mention this kind of wall, generally relegating it to the margins of “minor” architecture, that is, of those spontaneous constructions present in hills and mountains rich in stone, or along rugged coastlines (albeit less frequently).
Of course, when analysing the salient characteristics of rough stone masonry, we need to go beyond the configuration of the stone itself and focus on its other aspects, and in particular on the implications of the stonemason’s skills and knowledge.
The vocabulary associated with irregular masonry walls – a variation on the Romans’ masonry opus, which in turn is sometimes derived from Greek tradition – is always that of the informal arrangement of rough stones, of the incision along the stones’ edges represented by the contrast with the mortar joints (the latter often being intentionally “gauged out” or protruding, so as to highlight their separateness from the wall itself).
The choice of shape of the stones employed, together with their constructive arrangement (and thus their architectural design), furthers interest in the figurative qualities of the rustic wall – this primitive, essential construction, with its homogeneity, heaviness and thickness.

Canoe store in Pontecuti (1993-95) designed by Francesco Cellini

The material force of the stones and their woven arrangement within the wall are accompanied by an additional factor of vital importance from the figurative point of view: the way the joints between the stones are designed, that is, the distance left between one stone and the next. This crucial feature, where wider gaps than normal are left, to underline the singularity of each stone, is more evident than in other types of masonry wall.
Moreover, the mortar may be laid so that it remains below the surface of the stones (giving an indented effect), or it may be applied in such a way as to protrude with respect to the edges of the stones, or it may even be laid flush to the surface of the stones (thus covering a part thereof). In other words, the mortar pointing can either be clearly evident, thus highlighting the network of joints (which can be further accentuated by the use of mortar of a different colour from that of the stone), or somewhat “hidden” in the deeper recesses of the wall (as when set back into the gaps between the stones), thus marking the negativity and depth of the joints themselves, and capturing the light and its accompanying shadows. When we decide to emphasise the expressive force of the joints, we automatically underline their latent intrusiveness as well; both relief and engraving detract from the natural force of the stone itself to a certain degree, and for this reason, mortar joints should not be overemphasised.
In the case of this rather singular type of masonry wall – unlike that of walls built from square ashlars with their regular geometrical design already established at the planning stage – the real protagonist is the person who physically lays the stones and thus builds the wall: the “master” mason, the one person responsible for the constructive rhythms and appearance of the finished wall.
As Antonio Giuffré reminds us:
The opus quadratum wall, be it isodomic or pseudisodomic, is defined in a precise manner. The parallelepiped cut of the stones, their size and position in the wall, constitute immutable rules. The builder’s task consists in deciding the overall geometry of the wall and then strictly observing the said rules. (…). The stones in a medieval or a contemporary wall are very different, however, as they are not part of an overall design as the pentagonal ashlars in the Coliseum’s arches are, and they do not need to be accurately dressed and arranged as did the ashlars in the acrobatic weave of Gothic structures. The rough stone wall is not designed by the architect together with the overall architectural design of the building, but is built, one stone at a time, by a mason who, although no surveyor or architect, expertly follows the coherent logic underlying this kind of construction.
Before beginning work, he carefully examines the pile of stones he has to work with, and tries to remember their shape and size: the flat ones, the oblong ones, the irregularly-shaped ones. As he proceeds to lay the stones, he inserts stones according to the requirements of those already laid, alternating stones laid on their sides with those laid upright, filling gaps with those smaller pieces set aside, and using small wedges and shards to lay irregular stones as level as possible.
The wall rises in a more compact, ordered manner, the more skilful the mason; the latter adapts rough stone elements in order to create a horizontally-oriented, single structure, which in turn represents the fundamental requisite for the construction of a proper wall. ¹

Those aspects highlighted so far represent some of the general characteristics of the rustic wall. At this point, we may like to look closer at the various types of irregular wall.
Construction usually involves the laying of horizontal bands: first the external facing is laid, then the internal section of the wall is completed. Despite the informal character and irregular size of the various stones employed, such walls are not built without following any rules at all: on the contrary, such rules as exist have to be strictly observed, and in fact significantly influence the finished work.

Alfonso Acocella

Notes
* The re-edited essay has been taken out from the volume by Alfonso Acocella, Stone architecture. Ancient and modern constructive skills, Milano, Skira-Lucense, 2006, pp. 624.
¹ Antonino Giuffré, “La regola d’arte”, in Lettura sulla meccanica delle murature storiche (Rome: Edizioni Kappa, 1991), p.27.