The study looks at how the church as a dominant type of Rome led to the historical formation of the urban plan, while the piazza transformed from a religious to a secular public space. The open fields in Rome, demarcated as urban by the Aurelian wall, crystallised in Medieval Rome into autonomous centres of growth, when the erection of a church defined both a religious inner and secular outer space: the piazza. It subsequently created a polynodal network of inwards looking radial growth centres, of independent cities-within-the-city. These however lacked hierarchy and with a secularisation of the city, new planning instruments were required. The Renaissance street replaced the church as the formative urban element and restructured the city according to new political and administrative boundaries. The streets cut open existing, dense fabric and connected points of significance where no urbanity yet existed, establishing new urban lines and restructuring the city as a series of scenographic processions, often visually marked by monuments. While previously the piazza was defined as an exteriorisation of the church, the church had become a landmark or an element subservient to the public space.