The words on the pedestal imply that Ozymandias was a great ruler who believed his reign to be important to the history of man. The words read: "My name is Ozymandias, king of kings: Look on my works, ye Mighty, and despair!" Ozymandias thought the great statues built in his honor would last. He thought the great cities and temples and civilizations erected at his command would forever pay tribute to his importance as a man and as a king.
In fact, the poet tells us, all Ozymandias built has long since crumbled to ruin: "Nothing beside remains. Round the decay / Of that colossal wreck, boundless and bare / The lone and level sand." So, Ozymandias believed his work would last permanently. In the end though, he was wrong. All he built was impermanent: subject to ruin and decay, as is everything.