The main message of Shelley's “Ozymandias” is that political power is not destined to last. It is temporal, not eternal, no matter how powerful or fearsome a particular ruler may be. Even the most ruthless dictators will one day die, and what they regarded as their eternal achievements will also eventually pass on.

Thousands of years ago, a powerful pharaoh by the name of Ozymandias thought that his works would last forever. But in actual fact, he's left nothing behind to indicate the enormous power he must have exercised in his lifetime. All that's left to show that he even existed is a decaying statue of himself that's crumbling into the sands of the desert.

Shelley was a political radical and as such no respecter of powerful rulers. In presenting a stark picture of a pharaoh's crumbling statue, he wants to demystify the power of the ruling elite, to show people that it ultimately has no lasting foundations. Kings, queens, and pharaohs alike may want their subjects to think that they rule according to God's will, but in actual fact, they're just as human as the rest of us, no matter how high and mighty they may behave or how much power they seek to project.

Shelley uses irony to convey the message that the power of tyrants is fleeting and unstable. Tyrants may delude themselves that their kingdoms and power will last forever, but, in fact, this is not true.

To make his point, Shelley has the poem's speaker use the story of Ozymandias, an ancient ruler. The speaker has met a traveler who tells him of going to an "antique" or ancient land. There, amid a vast desert that spreads out as far as the eye can see, the traveler finds a broken statue of a once mighty, sneering king named Ozymandias. The statue has written on its pedestal the words

My name is Ozymandias, King of Kings;

Look on my Works, ye Mighty, and despair!

The meaning or themes of Percy Bysshe Shelley’s poem “Ozymandias” are fairly straightforward and are also highly traditional. Basically, the poem reminds powerful people that their power is only temporary. However much powerful people may wish to think that their power is immortal, they are only deceiving themselves. Earthly power is mutable, and indeed all human beings (Shelley may imply) need to remember this lesson.

What makes all these meanings highly memorable, of course, are the techniques Shelley uses, including the following:

• The speaker of the poem doesn’t himself preach; instead, he merely quotes the words of another person (the "traveller"), so that we are more likely to listen and consider the opinions the poem expresses. The speaker himself does not come across as a mere propagandist; rather, he presents himself as an honest reporter.
• Although the poem has obvious relevance to (and implications for) powerful people of the present day, Shelley keeps it from seeming a mere piece of contemporary political propaganda by making it a lesson about powerful figures of the past.  Readers are more likely to listen to a general moral lesson than to a lesson that seems aimed at particular political targets of the present.
• By keeping the poem short, Shelley gives it added impact and increases the likelihood that it will be read.  Few people have taken the time to read Shelley’s long political poems, but many, many readers have read and been moved by “Ozymandias.”
• By presenting this message about mutability in the form of a sonnet, Shelley deals ironically with a genre often associated with love.  However, Shakespeare’s sonnet 55 is similar in various ways to Shelley’s poem, as are various political sonnets by Milton and Wordsworth.
• Shelley uses extremely vivid and memorably imagery.  Rather than treating his topic in vague, abstract, or general terms, he creates highly specific images, as when the traveller describes a statue he has seen:

. . . “Two vast and trunkless legs of stone
Stand in the desert... Near them, on the sand,
Half sunk, a shattered visage lies, whose frown,
And wrinkled lip, and sneer of cold command,
Tell that its sculptor well those passions read
Which yet survive, stamped on these lifeless things . . . (2-7)

• Shelley uses irony when he lets Ozymandias speak for himself by reporting the inscription carved on the dead king’s crumbled statue:

‘My name is Ozymandias, king of kings:
Look on my works, ye Mighty, and despair!’ (10-11)

• Immediately after reporting these proud and now almost ridiculous words, the traveller merely observes: “Nothing besides remains” (12). Rather than spelling out the lesson for us, the traveller, the speaker, and Shelley all let us draw the obvious conclusions for ourselves. The poem thus shows respect for its readers' intelligence.