To be inscribed on the UNESCO World Heritage List, the UNESCO World Heritage properties must be of Outstanding Universal Value and meet at least one of ten selection criteria. The Three Castles, Defensive Wall and Ramparts of the Market-Town of Bellinzona meet criterion IV for the inscription.
Criterion (iv): The fortified ensemble of Bellinzona is an outstanding example of the late medieval defensive structure guarding a key strategic Alpine pass.
Integrity: The fortifications of Bellinzona have conserved intact their typical aspect of the late Middle Ages. Putting aside substantial losses to the wall and the ramparts of the town, the property comprises the ensemble of the conserved defensive works (castles, wall and ramparts) and thus retains all the requisite elements to express its Outstanding Universal Value.
Authenticity: The authenticity of the property is clearly witnessed by the numerous documents concerning its evolution. However, it has been affected to a certain degree by reconstructions, in particular the crowning of the walls, while the majority of the built substance is original and bears witness to developments over time. The use of the site is today cultural (museum, visits to the castles); the fortifications however represent a strong signification for the urban landscape and cultural environment.
You can find more information at whc.unesco.org.