Setting in this novel is incredibly important, because the ancient city of Casterbridge with its easily detected remnants of Roman civilisation act as a physical symbol of Michael Henchard and his past that he seeks to cover up. Note how Casterbridge is described in the following quote:

Casterbridge announced old Rome in every street, alley, and precinct. It looked Roman, bespoke the art of Rome, concealed dead men of Rome. It was impossible to dig more than a foot or two deep about the town fields and gardens without coming upon some tall soldier or other of the Empire, who had lain there in his silent unobtrusive rest for a space of fifteen hundred years.

Although surely the ubiquitous bodies of dead Romans and artefacts is a slight exaggeration on the part of the narrator, the setting bears many similarities to Henchard's character. The implication is that just as if you dig around in Casterbridge you can uncover its hidden past of a more ancient civilisation, so too Henchard's past, that he strives to keep secret, easily becomes uncovered and is exposed to the world. Just as the past of Casterbridge as a city cannot be escaped, so too Henchard's past is something that cannot be covered up successfully and is something that will be exposed.

How is the setting important in The Mayor of Casterbridge?

The Mayor of Casterbridge is one of Thomas Hardy's "Wessex" novels, set in a fictional county of Wessex that mirrors southwest England (especially Dorset). Hardy, who considered his novels mainly potboilers to support his work as a poet, uses the setting to evoke nostalgia for a rural England of the past, with "ye olde England" values of thrift, connection to the land, and harmony with nature. This idyllic rural vision is often realized in extended description of the appearances of old churches and other buildings in villages and landscape descriptions. Always, though, life in Wessex has a corrupt underside -- rape, cruelty, inequality, greed -- which is tearing communities apart from the inside as external connections such as the railroad and migration of labor destroy Wessex from the outside.