In Gothic architecture , a decorated circular window, often glazed with stained glass, that first appeared in mid-12th-century cathedrals.
It was used mainly at the western end of the nave and the ends of the transept . The bar tracery of a High Gothic rose window consisted of a series of radiating forms, each tipped by a pointed arch at the outside of the circle. The rose windows of Notre-Dame de Paris are particularly noteworthy. In later Flamboyant-style tracery, the radiating elements consisted of an intricate network of wavy, double-curved bars.