Shelley captures a summer dusk in Pisa that feels both drowsy and unsettled. The first lines picture sleep: swallows settled, bats skimming, toads creeping out, and a breeze so faint it leaves the stream’s “summer dream” untouched. But by the second stanza, the air grows dry and restless. There is no dew, and a light, inconstant wind drives dust and straws in circles over the paving stones. The mood hovers between stillness and quiet agitation.
The poem’s heart is the river’s reflection of the city—a “wrinkled image” that trembles continuously yet never fades. That paradox of permanent movement seems to hold the speaker’s attention. As dusk deepens, ash-grey clouds pile up like mountains, then part to reveal a pool of pale blue, pierced by the evening star. The closing lines suggest that while we change, this fragile, flickering scene endures exactly as it is. The whole poem breathes a delicate wonder at something constant inside the flux.