Simson Line If you circumscribe a triangle (ABC) and place a point (D) on that circle and then draw a perpendicular line from that point to each side of the triangle, 3 points of intersection (G,F, and E) are created. These three points are collinear, and the line that connects these point is the Simson Line.
Background: The concept of the Simson Line is named after Robert Simson, but was actually first published by William Wallace in 1799. Some call the Simson Line the Wallace-Simson Line because Simson did not in fact publish anything on the topic. It is a mystery as to why Robert Simson was credited with this theorem since William Wallace is the sole creator.