The Question and Answer section for Percy Shelley: Poems is a great resource to ask questions, find answers, and discuss the novel.
I think you are referring to the poem Ozymandias. An antique land would mean a very old land. This represents the long history as well as the mythic properties of Ozymandias.
I met a traveller from an antique land,
Who said—“Two vast and trunkless...
"Ozymandias" - ??? The statue, although now decomposed, represented the rule of one of the great Pharoahs. His rule covered a vast area of land and was thus not just large because of its size, but vast, because of its influence.
Sorry, I do not have the anthology you are referring to.