Shelley began writing his poem in 1817, soon after the announcement of the British Museum's acquisition of a large fragment of a statue of Ramesses II from the thirteenth-century BCE, and some scholars consider that Shelley was inspired by this. The 7.25-ton fragment of the statue's head and torso had been removed in 1816 from the mortuary temple of Ramesses at Thebes by the Italian adventurer Giovanni Battista Belzoni (1778–1823). It was expected to arrive in London in 1818, but did not arrive until 1821. Shelley wrote the poem in friendly competition with his friend and fellow poet Horace Smith (1779–1849) who also wrote a sonnet on the topic. Smith's poem would be first published in The Examiner a few weeks after Shelley's sonnet. Both poems explore the fate of history and the ravages of time—that all prominent men and the empires they build are impermanent and their legacies fated to decay and oblivion.
http://en.wikipedia.org/wiki/Ozymandias
http://en.wikipedia.org/wiki/Ramesses_II