SCIentific RESearch and Information Technology Ricerca Scientifica e Tecnologie dell'Informazione Vol 10, Issue 1 (2020), 53-66 e-ISSN 2239-4303, DOI 10.2423/i22394303v10n1p53 Open access article licensed under CC-BY-NC-ND CASPUR-CIBER Publishing, http://www.sciresit.it SOME RECONSTRUCTION HYPOTHESES OF LEONARDO’S PROJECT FOR THE TIBURIO OF THE MILAN CATHEDRAL BY USING 3D DIGITAL MODELS Sabine Frommel*, Fabrizio Ivan Apollonio**, Marco Gaiani**, Gianna Bertacchi** *École Pratique des Hautes Études, Sorbonne - Paris, France **Department of Architecture, Alma Mater Studiorum University of Bologna - Bologna, Italy. Abstract This paper analyses possible interpretations of the unbuilt Leonardo's project for the tiburio of the Milan cathedral, depicted in two sheets of the Codex Atlanticus, using digital tools, mainly 3D modelling techniques. Starting from existing studies and hypothetical reconstructions of Leonardo’s project, exploiting only analogue methods (i.e. 2D drawing techniques), new in- depth analyses are presented. In detail the use of 3D modelling allows a systematic analysis of the possible solutions for the ability to easily reconstruct the plan of each solution investigated starting from the section represented by Leonardo in the Codex Atlanticus. Results lead to multiple interpretative solutions of this complex architecture. Keywords Leonardo da Vinci, Tiburio, Cathedral, Milan, Unbuilt architecture, Virtual reconstruction, 3D modeling. 1. Introduction these two sheets. The information that several other sketches provide regarding this project is The present contribution analyses some also limited. possible reconstructions of Leonardo’s project for Even if these sketches tell us that Leonardo, the tiburio of the Milan cathedral using digital during his entire life, carried out in-depth studies tools, mainly 3D modelling techniques. upon that matter, always referring to ancient and In 1487 the Milan authority for the contemporary architecture and analyzing also construction of the cathedral, the Fabbrica del structural problems and practical constructive Duomo, asked architects and engineers for a solutions (Firpo, 1963; Maltese, 1975; Frommel, proposal of completion for the tiburio and the 2019), however no decisive contribution is given solution of a structural problem concerning the to research about his real conception of the tiburio. main pillars (Beltrami, 1903; Pedretti, 1978). This ambiguity generated over time different Leonardo gave a detailed proposal displayed in interpretations, both in the project as a whole and two sections/projections drawn on two different in the details of the structure. paper sheets today classified as f. 850r and f. 851r The aim of a new study of the subject of these of the Codex Atlanticus (CA), and at least in one two drawings using digital reconstruction tools is, wooden model, today lost. then, to understand Leonardo's project (Fig. 1), Leonardo's drawings are complex plots not limiting the misunderstandings of the translation allowing an easy reading, both for the lack of an of the two-dimensional into 3D, and analyzing only associate plan and for the difficulty to distinguish a small group of different, but consistent and valid between section and foreshortened elevation, interpretations of Leonardo’s design. most likely coexisting, to which is added the Digital techniques, mainly the use of 3D presence of pricked marks of the pouncing modelling systems, allow a systematic analysis of technique, which therefore indicate a true size of Leonardo’s possible intentions for their ability to proportions, even of those elements that should be easily reconstruct the plan of each solution foreshortened (for example the ribs of the vaults). investigated starting from the section. More, The fact that the project was never built digital vector-based representations allow to contributes to the difficulty of understanding how he imagined the solution for the tiburio figured in (2020), n. 1 S. Frommel, F. I. Apollonio, M. Gaiani, G. Bertacchi Fig. 1: Comparison between the 3D reconstruction and an edited detail of the f. 850r, Codex Atlanticus. quickly generate multiple solution variants Sun, 2013; Apollonio, 2016; Frommel, Gaiani, & viewable in 3D and then both in elevation (as Garagnani, 2018): the analysis of different data Leonardo’s tiburio drawings) and in plan. sources, the formulation of some conjectures by In detail, the 3D-based method used follows a deduction or induction and their consequent well-defined workflow for the reconstruction of no iterative verification, led to the definition of two more existing or unbuilt architectures grounded in “most probable” solutions. shared working hypotheses, and our specific The first one follows and deepens the solutions (Steadman, 1989; Apollonio, Gaiani, & analogical reconstruction proposed by Jean 54 (2020), n. 1 Some reconstruction hypotheses of Leonardo’s project for the tiburio of the Milan cathedral Guillaume and Sabine Frommel in 1987 2. Leonardo & the tiburio (Guillaume, 1987). The second solution arises from a new and completely different During his stay in Milan at the court of interpretation of Leonardo's drawing and, while Lodovico Sforza, from 1487 until 1490, Leonardo presenting some common parts with the first, explored the topic of centralized churches determines a very different structural output. systematically and in the process classified them in his drawings according to typological and morphological principles (Guillaume, 1987, pp. 224-245; Frommel & Guillaume, 2019, pp. 35-41). These drawings of the Manuscript B (Institut de France, Paris) provide an important contribution to one of the more fascinating themes of the Renaissance. Main axes and diagonal spaces characterize a lot of those ideal projects, but the artist was also highly interested in unified systems. The sketches are represented both as plans and three-dimensional renderings, in the form of perspectives, bird’s-eye views or axonometries, which allow to control the whole organism in a highly efficient way. An original approach, that reveals that he looked at architecture as a whole. No other drawings of the sort by any contemporary architect survive, however it’s Fig. 2: 2D definition of the pointed arch, that has been possible that Leonardo conceived these drawings regularized by dividing its length into 10 segments in addition to the keystone; each part has been divided in dialogue with Donato Bramante, who was active transversely into three equal segments to define the in Milan at the same time, designing spectacular tongue and groove joint. churches such as Santa Maria presso San Satiro and Santa Maria delle Grazie (Giordano, 1998, pp. 183-186). In any case, the latter seems to draw on The 3D models were defined following a these variations of the theme of central plans when methodological approach based on a well-defined he designed the reconstruction of Saint Peter in workflow starting with the transposition of 1505 for Julius II. And, vice versa, one cannot Leonardo’s sheet into a 2D CAD reference exclude that Leonardo, his long-lasting friend, was drawing1 (Fig. 2), followed by the integration of also involved in the Roman design (Frommel, the information derived from surveys of the 2019, pp. 101-102). Duomo (Beltrami, 1903; Ferrari da Passano, In the same Milanese years, Leonardo faces the 1973)2. Then all these 2D inputs are translated in completion of the tiburio of the cathedral of Milan, 3D and, finally, the rough model is completed the tower-like construction that, according to the shaping the smallest elements, like ashlars and Lombard tradition, crowns the crossing (Schofield voussoirs. 1989; Frommel 2019, pp. 68-75). In the specific case of the tiburio, the approach The building-site had started in 1386, and by allowed to deduce the plans of the two hypotheses, 1480 the vaults of the crossing, the choir and five starting from the common main section (the bays of the nave had been achieved. Now emerged representation of Leonardo). We can notice that the tricky problem: how to erect a tiburio 50 this procedure inverts the Vitruvian procedure in meters tall on slender pillars and fragile arches. which the elevation is derived from the plan (from The task was very challenging. Though the tiburio ichnographia to orthographia; Bartoli, 1978; Dezzi was a traditional Lombard solution, it had never Bardeschi, 2017, pp. 91-92). 1 The reference drawing used for the creation of the 2D base measurement used at the time of the project, i.e. the braccio is the sheet 850r of the CA, which seems to be a more milanese, equal to 0.594936 meters. The interaxle spacing definitive version of Leonardo's project in terms of detail. between the main pillars, equal to 19.2 meters, i.e. 32 braccia 2 The validation of proportions was carried out milanesi and 4 once, was taken as the principal reference simultaneously with the verification of the ancient units of measure to scale the entire drawing. 55 (2020), n. 1 S. Frommel, F. I. Apollonio, M. Gaiani, G. Bertacchi before taken such breath-taking dimensions! used to report the measurements directly on the Sebregondi, Gritti, Repishti, & Schofield (2019) wood to construct the model. Soon afterwards the formulated some hypotheses which, however, the model was ready, but in May 1490 he took it back references considerered in this solution are not again in order to improve other details, these those proposed here. additional modifications were also paid by the In 1481, after the death of Guiniforte Solari,