The Pentagon as the Constructed Form of the City

Abstract

[EN]The effectiveness of fortresses, until the fifteenth century, was tied to their height, as the most effective defensive actions involved the pouring of boiling objects and liquids from above. The subsequent development of heavy portable artillery systems questioned the traditional form of fortification, characterized by walls perpendicular to the ground. This recognition, found in the writings of Leon Battista Alberti in "Re Aedificatoria," emphasized that to increase effectiveness, defenses should be constructed along irregular lines, like the teeth of a saw. With Antonio and Giuliano da Sangallo, military architecture became a branch of geometry, and debates regarding the correct number of bastions to provide the best defensibility sparked numerous discussions in the transition between the fourteenth and fifteenth centuries. The radiocentric form, typical of the Renaissance city, was one of the reasons that led to the choice of the pentagon as a design solution for fortifications, as obtuse angles, unlike right angles, allowed for greater resistance to splaying.This very form became the generative element of the urban development of the city of Livorno, coinciding with the urban plan drafted by Bernardo Buontalenti. In the mid-1500s, Francesco I de' Medici decided to expand the town of Livorno, incorporating a new inhabited center within a system of powerful fortifications surrounded by a canal, giving the city a pentagonal shape, with the hypothetical center being the Cathedral. Thus, the pentagon, part of Buontalenti's design, now visible in the course of the canals surrounding the core in the water, built by Venetian craftsmen, became the city's form.