In "Ozymandias," the speaker recounts what he heard from a traveller from an ancient land. Shelley uses apostrophe here, a poetic technique where the speaker addresses an imaginary person, abstract quality, or an idea. Apostrophe means "turning away" as if the speaker/poet directs his speech to the air, like a prayer or philosophical inquiry.
He meets the traveller who tells him of a monument he saw which was eroded to the point that only two legs were left standing. Beside the bodiless legs lies a half buried face (visage) with a smirk on it. In the next lines, he notes that the sculptor accurately and mockingly captured this ruler's pride and pomposity:
Tell that its sculptor well those passions read
Which yet survive, stamped on these lifeless things,
The hand that mocked them, and the heart that fed;
The king's (Ozymandias, the Greek translation for Ramses II) heart had fed on those passions. And the sculptor's hand mocked them. Ironically, it is the sculptor's work, not the king's, which has stood the test of time. Unfortunately for the sculptor, the monument has been reduced to a "colossal wreck" surrounded by a barren land. The words inscribed on the ruin's pedestal parallel the pretentious smirk on the kings visage. The erosion and decay of the monument enforces the satire that this once proud king's memorial is now humble and neglected.