I agree with the comments of others here, this nomination makes little sense, the city of Valletta is already a UNESCO site, it's a tiny city, the smallest capital in Europe, and the fortifications are an integral part of the city.
It looks like an attempt to draw more tourists in to be honest.
Don't misunderstand me, the fortifications are impressive and made from that beautiful honey coloured stone that makes Malta so unique but it would be a travesty to get a separate listing when many places in need of inclusion are left out.
Many cities do have multiple listings, London and Paris are just a couple of examples, the difference here is that the whole city of Valletta is a UNESCO site so it already encompasses all elements.