Theme of transience
Ozymandias is obsessed with transience; the very fact the statue is a colossal wreck" 13 says loudly and clearly that some things just don't last forever. But the poem isn't just about how really bnig statues eventually succumb to the ravages of times; the statues is a symbol of Ozymandias's ambition, pride, and absolute power, and thus the poem also implies that kingdoms and political regimes will eventually crumble leaving no trace of their existence except, perhaps, pathetic statues that no longer even have torsos