These are the stories that the Dogs tell when the fires burn high and the wind is from the north. Then each family circle gathers at the hearthstone and the pups sit silently and listen and when the story's done they ask many questions:
"What is Man?" they'll ask.
Or perhaps: "What is a city?"
Or: "What is a war?"
There is no positive answer to any of these questions.
Clifford D. Simak's City (1952) is an example of a fix-up: a collection of related short stories. Sometimes a fix-up will include a framing story to provide it with a greater sense of overall unity. City has such a framing story, as do other SF works such as Isaac Asimov's I, Robot (1950), Gordon R. Dickson's The Spirit of Dorsai (1979), Robert Silverberg's Majipoor Chronicles (1982), and Larry Niven's Crashlander (1994). (Notable examples of fix-ups without framing stories are Ray Bradbury's The Martian Chronicles  and Arthur C. Clarke's Tales from the White Hart .)
The parallels between City and I, Robot are particularly close. All but one of City's eight stories first appeared in Astounding Science Fiction during that magazine's "golden age" of 1939-1950, as did all but one of I, Robot's nine stories.* Both books were published in the early 1950s by a small genre publishing house called Gnome Press. Simak and Asimov were both notable "Campbell authors" who first gained prominence within science fiction due to their regular appearances in the pages of John W. Campbell's Astounding. Finally, Simak and Asimov were friends who corresponded regularly with each other over the course of their lives (though their meetings were infrequent due to their geographic separation).
In a Foreword to City written in 1976, Simak states that the stories that make it up were the result of his disillusionment with the coming of World War II. "There was, it seemed, no limit to the horror that men would inflict on one another." Although Simak's disillusionment was originally the product of the war itself, and not the arrival of nuclear weapons, he states that"Hiroshima and Nagasaki served only to confirm and deepen the disillusion."
In writing the stories, Simak says he was "seeking after a fantasy world that would serve as a counterbalance to the brutality through which the world was passing. Perhaps, deep inside myself, I was trying to create a world in which I and other disillusioned people could, for a moment, take refuge from the world in which we lived."
The stories in City follow the world through twelve thousand years of future history, as the human race grows in power, before abandoning the Earth, leaving it in the possession of robots and uplifted dogs. The first story, "City", set in 1990 and first published in the May 1944 issue of Astounding, shows the decay of urbanism as people abandon the cities to live in isolated estates where all the maintenance work is done by robots. "City" introduces the character of John J. Webster, the ancestor of most of the human characters in the later stories.
The second story, "Huddling Place", is set in 2117 and was first published in the July 1944 issue of Astounding. "Huddling Place" tells the story of Jerome A. Webster, the great-great-grandson of John J. Webster. Jerome is a surgeon who is called upon to travel to Mars to save the life of Juwain, a brilliant Martian philosopher. However, Jerome is afflicted with agoraphobia, the result of spending most of his life living on the rural estate established by his great-great-grandfather, and finds it impossible to leave. This story introduces the character of Jenkins, the Websters' household robot, who will appear in most of the later stories.
The third story, "Census", is set in 2183 and was first published in the September 1944 issue of Astounding. Jerome's grandson Bruce is burdened by his grandfather's failure to save Juwain's life. He has devoted his life to uplifting his dogs, hoping to make up for his grandfather's failure by giving humanity a companion race with a complimentary viewpoint. "Census" introduces the character of Joe, a mutated human with enhanced intelligence and an extended lifespan. In his Foreword Simak reveals that Nathaniel, the first of Bruce Webster's uplifted dogs, was based on Scootie, Simak's beloved Scottish terrier, to whose memory City is dedicated.
The fourth story, "Desertion", is set around the year 3000 and was first published in the November 1944 issue of Astounding. The story leaves the Websters and looks in on a small human base on the surface of Jupiter. Kent Fowler is in charge of a project that transforms men into an intelligent Jovian race called Lopers and sends them out to explore Jupiter. So far, five men have gone out, and none has reported back. Fowler finally decides to go through the transformation himself, together with his dog Towser (who is not one of Bruce Webster's uplifted talking dogs, but simply a standard-issue tail-wagging dog). After becoming a Loper, Fowler finds that the surface of Jupiter is a wonderful place to be, and that being a Loper is much more enjoyable than being a man (and he can also talk with his Loperized dog). The reason the men he sent out failed to come back was because they didn't want to go back to being human. Fowler realizes that he doesn't want to go back, either.
The fifth story, "Paradise", is set five years after "Desertion" and was published in the June 1946 issue of Astounding. Kent Fowler's sense of duty has compelled him at last to return to human form and report back to his superiors. This presents a problem for Tyler Webster, the head of Earth's government. Webster knows that if Fowler's story gets out, the human race will abandon its civilization and retire to Jupiter. His efforts to bury Fowler's story are thwarted by Joe the mutant, who has worked out Juwain's lost philosophy and unleashes it on an unsuspecting humanity. After being exposed to Juwainism, Webster realizes that it would be wrong to keep Fowler's revelation hushed up. He must let Fowler tell his story, even though it will mean the end of human civilization.
The sixth story, "Hobbies", is set around the year 4000 and was published in the November 1946 issue of Astounding. The only humans left on Earth are a small enclave located in Geneva, led by Jon Webster, and a few scattered naturalists led by Webster's son. The rest of the planet has fallen by default to the Dogs, descendants of Bruce Webster's uplifted dogs, aided by an army of robots. Jon Webster makes a trip back to his ancestral homestead in North America. After talking to a Dog named Ebenezer and to Jenkins, the leader of the robots, he learns that the Dogs have discovered a series of alternate dimensions they call the cobbly worlds. Webster realizes that the new civilization established by the Dogs and the robots deserves a chance to develop free from human interference. He returns to Geneva, sets off an ancient defence mechanism that isolates it and its human inhabitants from the rest of the world, then retires to a permanent state of suspended animation.
The seventh story, "Aesop", is set around the year 9000 and was published in the December 1947 issue of Astounding. The Dogs have undertaken the task of uplifting and civilizing the rest of the animal kingdom, creating a civilization they call the Brotherhood of Beasts. When one of the few remaining humans reinvents the bow and arrow and inadvertantly kills a robin, Jenkins realizes he must lead the last of the humans to one of the cobbly worlds, lest they reintroduce warfare to the world and destroy the Brotherhood of Beasts.
The eighth story, "The Simple Way", is set around the year 14,000 and was published in the January 1951 issue of Fantastic Fiction under the title "The Trouble With Ants". Jenkins returns to the world of the Dogs to find that a new threat to the Brotherhood of Beasts has arisen: a colony of uplifted ants established long before by Joe the mutant is slowly remaking the world. Remembering that men once had a simple way of dealing with ants, Jenkins travels to Geneva and communicates with Jon Webster, who is still in suspended animation. Webster informs Jenkins that the human way of coping with ants was to poison them. Jenkins decides that the human way is not his way; he will lead the Dogs and robots to another cobbly world, leaving the Earth to the ants.
When Simak assembled the City stories for book publication in 1952, he created a framing story in which a Dog academic who is editing the book discusses the vexing question of whether the stories (a set of popular legends among the Dogs) are purely mythical, or whether they have some basis in truth. In particular, he discusses the question of whether the race of Men they describe was real or not. The editor notes the contending views of three important Dogs: Rover and Bounce, who believe that the stories are mythology and nothing else, and Tige, who believes that the stories have a historical basis, and that the earliest ones were actually composed by Men rather than Dogs.
Twenty years after the publication of City, science fiction writer and editor Harry Harrison was moved by the death of John W. Campbell to assemble a memorial anthology called Astounding, featuring new stories by notable Campbell authors such as Isaac Asimov, Theodore Sturgeon, and of course Clifford D. Simak, whose contribution was a final City story called "Epilog". This story is set in the far future, when the Earth's only inhabitants are the ants, some mice, and Jenkins the robot. The Dogs have led the other animals to one of the cobbly worlds, and the ants have covered the whole world with a single vast city. The only remaining open area is a circle ten miles in diameter centered on the Webster House that the ants have left alone for some inscrutable reason of their own. When the Dogs left Jenkins remained behind to maintain the Webster House, and the mice decided that they preferred to stay where they were. Jenkins' solitary vigil is interrupted by two events. First, the ants' city starts to fall apart, and Jenkins discovers that the ants have died out. Second, a spaceship crewed by robots lands and asks Jenkins to join them. When Jenkins realizes that even his robotic memories of humanity is fading, he decides to leave with the other robots. His only regret is that, being a robot, he cannot weep for the abandoned Earth.
*Sadly, none of Simak's City stories ever appeared in the same issue of Astounding as one of Asimov's Positronic Robot stories. Such is life.