To be included on the UNESCO World Heritage List, it is necessary to demonstrate that the nominated property has an Outstanding Universal Value. What makes the concept of World Heritage exceptional is the fact that the listed properties belong to all the peoples of the world, beyond the territories in which they are located.
Bologna boasts an extension of porticoed stretches equal to 62 kilometers, unrivalled in any other place in the world. It is also extraordinary that the porticoes have been built in the city since the 12th century to the present day, without a break, thus creating a veritable catalogue of architectural forms differing in style, materials, building type, function and urban role. In many other cities in Italy, in Europe and in the world, the portico is present, but nowhere in such a pervasive and varied way as in Bologna.
Porticoes in Bologna could withstand a long period of time and become an element of identity for the city as well as a place for socializing and relationships, thanks to a regulatory system that obliged the owners to build porticoes and the legal nature of the portico as a private space for public use. Even today whoever walks through Bologna can find a variety of exceptional porticoed architecture. On the other hand, this urban feature has always struck passing travellers, artists and scholars, who then contributed to exporting the Bolognese portico model and its spreading throughout the world.
The 12 nominated components are all necessary for the complete representation of the values of the Bolognese porticoed system, since each of them has specific characteristics both for its architectural typology and for the role it plays within the city.