“Ozymandias” has two primary settings. The first is an unspecified time and place—most likely, early 19th century England when the poem was written—where the speaker and the traveller meet. The second is the recent past in Egypt, where the traveller sees a ruined statue of Ozymandias in the desert. The poem only spends a line and a half on the first setting, devoting the remaining twelve and a half lines to the desert scene: by focusing on nature and the crumbling remnants of a statue, the poem shows how nature can destroy everything human-made, from political systems to statues, and yet how art, even when broken, can provide a kind of artistic immortality.

It's worth noting that if one subscribes to the theory that the traveller to whom the speaker refers is actually Diodorus Siculus, an ancient Greek writer whose description of an actual destroyed statue inspired Shelley's poem, then the settings of the poem subtly shift. In this case, the first setting is any location in which the speaker can "meet" Siculus (i.e. by reading Siculus's passage in a book), while the second setting is still the desert in Egypt, but it is Egypt not during Shelley's time but rather during the time of the ancient Greeks.