Congruent Illusions - Many of these illusions date back over 100 years, and involve identical lines or circles that appear to differ. Greater detail and other interesting topics are discussed at Eluzions.com

This classic illussion depicts equal length horizontal lines in the two figures.	The top sides of these two trapezoids are equal in length.
The V in this parallelogram has equal length legs.	The inner circles in these two figures have equal diameters.