What does decayof that colossal wreck mean ozymandias?

In "Ozymandias" by Percy Bysshe Shelley, the phrase "decay of that colossal wreck" refers to the ruins of a once-mighty statue of the Pharaoh Ozymandias, symbolizing the inevitable decline of all leaders and empires. Despite Ozymandias's grand ambitions and the inscription proclaiming his greatness, the statue lies shattered and eroded, highlighting the transient nature of power and human achievement. This decay serves as a reminder of the passage of time and the futility of arrogance in the face of mortality and nature's forces.