Geometry in Art (project help needed!)

I've spent countless hours brooding over this damn project, how geometry is used in art.

If you could give me some kind of input on how geometry is used in art, that would be grande!

We need to fill 20 min. presentation with a homework assignment and in class activity.

The topics we are already discussing are greek, roman and renaissance architecture, modern architecture (new seattle public library), photography's rule of thirds, tessalations, MC Escher, and perspective in renaissance paintings. Though more information on all these topics and any others would be wonderful (esp. perspective)!

Thank you!