Describe the theme of the poem "Ozymandias."

"Ozymandias" is an 1818 sonnet by the English poet Percy Bysshe Shelley, a major player in the English Romantic movement. In it, Shelley describes meeting a traveler from an "antique land" who tells him of the remains of a statue of the king Ozymandias inscribed with the title "king of kings" and the phrase "Look on my works, ye Mighty, and despair!"
Ozymandias is a Greek name for the Egyptian pharaoh Ramesses II, typically remembered as the greatest of the pharaohs. The statue referenced in the poem would have been one of many monuments left behind by Ramesses, who ruled for decades and would have very much been the "king of kings" in his time. However, by the nineteenth century, this statue has collapsed. Shelley describes the two legs as the only part still standing, with the head half buried in the sand. Around the ruins of the statue "nothing beside remains." Ozymandias, or Ramesses, for all his glory in life, has little to show in the millennia since his death. 
Shelley is exploring the ideas of impermanence and the inevitable decay and decline of all things. By focusing on one of the greatest kings of one of the world's greatest and most enduring societies, he is showing that even the mightiest of kings will one day decay and be forgotten. Shelley's tone suggests that he is reprimanding Ozymandias for his hubris and is warning the reader against delusions of immortality. No matter what we accomplish, we will all one day be like Ozymandias, with our legacy falling apart and breaking down.