[Sephiroth]

Using the genitive case for lamentation, I think it would be:

civitas ploratiae (or urbis ploratiae)

or

civitas luctae (or urbis luctae)

Ploratio is mourning, weeping, lamentation in a more personal sense, I think. Luctus is lamentation, mourning, grief. It would take an expert, like Giovanna Clairval, to tell you what is more appropriate.