During that time when it was like quiet time so street probably then at night nobody was roaming the streets then they were at home. The fog is personified in the image of a cat. They both have the same characteristics such as unexpected silence, and quietly  without warning. As a cat soundlessly creeps on a window ledge, so does fog roll in unexpectedly over the city.

Anthony, I know what the poem means - you need to tell me how the events that were happening historically inspired the poet.