Irony is a literary technique that allows a writer or poet to express him or herself in a unique way. It allows for a broad understanding of a possibly otherwise uninspiring description and creates a visual picture, often amusing and always significant. A reader becomes aware that an emphasis is being placed on something and can appreciate aspects of writing that they may otherwise overlook. There are different types of irony: dramatic irony, verbal irony, and situational irony.
In dramatic irony, the reader or audience is aware of something that the characters are not. In verbal irony, something is said that is contrary to its real meaning and with situational irony, what is intended and what actually takes place are not the same. Situational irony is about expectations.
In Ozymandias it is apparent that the great ruler expects to be remembered in history. His statue reveals that he may once have been a feared ruler with a "sneer of cold command." However, the traveler recognizes his "frown and wrinkled lip" as being the only recognizable features of this "shattered visage." Ironically, although the ruthless character may be apparent from the image sculptured by the sculptor, it is only apparent on this "lifeless" statue and certainly not in the surroundings. The situational irony exists in the fact that the statue is supposed to express Ozymandias's great importance but all it reveals is his wretched and pitiful state and his inability to create and sustain the empire of which he apparently sought to be master. The plaque which reads "Look on my works..." is something that would make any self-respecting person ashamed. From a position of situational irony, his expectation of a greatness far beyond his life and which others, he thinks could only wish to emulate reveals his bigotry and self interest and does not reveal his presumed greatness. Ozymandias expects his statue and his "works" to show what a powerful man he is and will be forever and not what a contemptible person he must have been.