The Porticoes of Bologna has been declared today as World Heritage (even if Rick Steve's doesn't like this city).
Candidate since the 2006, Bologna finally has been accepted, after a long and troubling process. This webpage is about the process, but with a very good explanation: https://whc.unesco.org/en/tentativelists/5010/
Is important to say that the style of porticoes affect even other cities in Emilia-Romagna and in general northern Italy. So you find several porticoes even in Modena, Reggio Emilia, Parma, Cesena, Padua (and several towns and villages), by was called "Bologna style" since century.
BTW: has been declared even the Scrovegni's Chapel in Padua World Heritage. Unbelievable hasn't been just on the list since the beginning!