Cities can be seen as symbols of progress because they are usually centers of commerce and leaders in fashion and new trends. Most major cities also house universities, which often generate new ideas in economics or science. Because so much wealth is concentrated in cities, they become symbols of the new. For example, Florence in the 1400s and 1500s patronized artists and architects to such a great extent that the city became the symbol of the Renaissance. Its buildings, sculptures, and paintings became renowned for their innovations and high quality. Likewise, Weimar Berlin in the 1920s became a center and symbol of avant-garde art and architecture.
At the same time, the wealth in cities also attracts criminals. Cities are known for having areas where prostitutes function, and for areas of squalor associated with violence, abuse, and neglect. Cities can be dirty and unpleasant. All of this is associated with moral decay. Further, as Weimar Berlin illustrates perfectly, the innovations in art and culture that represent progress can also be so threatening and so ahead of their times that average people recoil from them and associate them with moral decay.