The high road into the village of Weydon-Priors was again carpeted with dust. The trees had put on as of yore their aspect of dingy green, and where the Henchard family of three had once walked along, two persons not unconnected with that family walked now. (3.1)
Susan and Elizabeth-Jane are walking along the same road that Susan traveled with Henchard the day that he sold her. The narrator uses words like "again," "of yore," and "once" partly to connect the past with the present and perhaps to emphasize how connected things are, even across the years.
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. (11.2)
Casterbridge is very much connected with the ancient past. Even though people don't think too much about it, their town is sitting on the ruins of a Roman city. There are skeletons under their town, not to mention in their closets. Like Henchard's personal past, the city's past is hidden just below the surface, and just a tiny bit of digging will expose it.
They had lived so long ago, their time was so unlike the present, their hopes and motives were so widely removed from ours, that between them and the living there seemed to stretch a gulf too wide for even a spirit to pass. (11.3)
The narrator suggests that the ancient Roman inhabitants of Casterbridge were totally unlike the people there now. Their "hopes and motives" were totally different from "ours." Do you think this is true? Do you think the narrator is being serious or ironic?
She began the study of Latin, incited by the Roman characteristics of the town she lived in. (20.30)
Elizabeth-Jane starts learning Latin because she's inspired by all the Roman history around her. It's a small detail, but it's another example of the way the past can influence the present.
She seized on these days for her periodical visits to the spot where her mother lay buried – the still-used burial ground of the old Roman-British city, whose curious feature was this, its continuity as a place of sepulture. Mrs. Henchard's dust mingled with the dust of women who lay ornamented with glass hairpins and amber necklaces, and men who held in their mouths coins of Hadrian, Posthumus, and the Constantines. (20.32)
Here's another example of the ancient Roman history of the town mingling with the present. The Roman dead share the same burial ground with the recently dead; their dust "mingles."
I won't be a slave to the past – I'll love where I choose! (25.24)
Lucetta tries to break with the past and escape it. Of course, that doesn't work out so well for her.
Had the incident been well known of old and always, it might by this time have grown to be lightly regarded as the rather tall wild oat, but the single one, of a young man with whom the steady and mature (if somewhat headstrong) burgher of to-day had scarcely point in common. But the act having lain as dead and buried ever since, the interspace of years was unperceived; and the black spot of his youth wore the aspect of a recent crime. (31.1)
Because Henchard doesn't tell anyone about the wife sale when he first arrives in Casterbridge, when the truth comes out many years later, it's as though it happened yesterday. The news is new, and so the long intervening years don't temper it.
Her figure in the midst of the huge enclosure, the unusual plainness of her dress, her attitude of hope and appeal, so strongly revived in his soul the memory of another ill-used woman who had stood there and thus in bygone days, and had now passed away into her rest, that he was unmanned, and his heart smote him for having attempted reprisals on one of a sex so weak. (35.17)
Henchard's meeting with Lucetta at the Casterbridge Ring is an echo of his meeting with Susan there. The two scenes have a lot of parallels, and Henchard senses it himself.
A quarter of a mile from the highway was a pre-historic earthen fort, of huge dimensions and many ramparts, within or upon whose enclosures a human being, as seen from the road, was but an insignificant speck. (43.9)
The ancient fort the narrator describes is prehistoric – it's even older than the ancient Roman ruins around Casterbridge! In part because of its size, but also because of its extreme age, the fort makes "human beings" seem "insignificant" next to it.
Hither Henchard often resorted, glass in hand, and scanned the hedgeless Via – for it was the original track laid out by the legions of the Empire – to a distance of two or three miles, his object being to read the progress of affairs between Farfrae and his charmer. (43.9)
Again, the past and the present collide here: the road Farfrae and Elizabeth-Jane walk on is the ancient Roman Via, or road. They're walking where many "legions" of Roman soldiers walked before them.