Answer: The statue is of a once powerful leader.
Source material refers to a document, artefact, diary, manuscript, monument, recording or any other type of material that gives us information on a topic we are studying. In this case, the monument to Ozymandias is a source of information on the ruler and his kingdom, and this helps Shelley develop his poem.
Moreover, we know that the traveller is not the person who carved the stone. The statue might be breathtaking, but that is not relevant to the question. Finally, there is no ritual associated with being able to see the statue.
