Tympanums architectural- What sets these wonders apart?
A tympanum is a decorative wall surface above a window or dor way, commonly in the form of a triangle or semi circle. This type or decorative architecture is usually not structural.
The picture below shows a triangle shaped tympanum.
The picture below shows a semicircle shaped tympanum.
Another image of a typanum topped window opening, taked from an upper perspective follows for reference.
The double window header in the image below shows roman arches which are actually structural support headers.