Regola and Licentia in the Extraordinario Libro by Sebastian Serlio

The Extraordinario Libro by Sebastiano Serlio, published in Lyon in 1551, is an interesting field of experimentation for the dialectical relationship, central to the Mannerist period, between Regola (Rule) and Licentia (License). This volume is composed of copper plates engraved with rich captions: “there are thirty doors of rustic work mixed with different orders: and twenty of delicate work of various species” (Serlio 1551: Frontispice). The book, not foreseen in the original editorial plan for drafting an architectural treatise, is tied with Book IV, concerning architectural orders, which was the first to be published in 1537. Indeed, in the monumental door, or portal, the architraved or arched entrance combines with the order to form an architectural element with a specific functional, formal, and decorative character (Chitham 1985: 99-101). In the twentieth century, the Extraordinario Libro was the object of some historical-critical studies that highlighted the character of “strange collection of portals and capricious cartouches” (Rykwert, in Carpo 1993: 7). However, there are no studies that analyze the geometric structure of the Serlian models, linking them to the modularity of the orders and to the unit of measurement of the period. The authors of this paper have undertaken this path with the aim not only, as in Fiore’s auspices, “to reproduce, following the text, the proposed graphic examples” (Fiore, in Serlio 2001: 17), but also to interpret, represent, and finally relate the proportional criteria underlying the iconographic corpus of the book. The geometric-modular relationships that rule the composition of the fifty portals are investigated using graphical analysis, which involves recognition, de-composition and re-composition of the elements, and philological reconstruction, aiming at: – comparing and classifying Serlian models; – identifying variants and invariants between proportions of ‘rustic’ doors and ‘delicate’ doors; – establishing connections to the rules of orders stated by Serlio in Book IV; – highlighting recurrent and exceptional compositional criteria.