Topic summary
Bar tracery

Extracted from the Wikipedia article Tracery.
Bar tracery
At the beginning of the 13th century, plate tracery was superseded by bar tracery. Bar tracery divides the large lights from one another with moulded mullions. Bar tracery, an important decorative element of Gothic styles, appeared first at Reims and was employed in England around 1240. After 1220, master builders in England had begun to treat the window openings as a series of openings divided by thin stone bars, while before 1230 the apse chapels of Reims Cathedral were decorated with bar tracery with cusped circles (with bars radiating from the centre). Bar tracery became common after c. 1240, with increasing complexity and decreasing weight. The lines of the mullions continued beyond the tops of the window lights and subdivided the open spandrels above the lights into a variety of decorative shapes. Rayonnant style (c. 1230–c. 1350) was enabled by the development of bar tracery in Continental Europe and is named for the radiation of lights around a central point in circular rose windows. Rayonnant also deployed mouldings of two different types in tracery, where earlier styles had used moulding of a single size, with different sizes of mullions. The rose windows of Notre-Dame de Paris (c. 1270) are typical.